Columbia  (Hnftttfitp 

intljeCttpofiJtogork 

College  of  ^(jpgtcians;  anb  burgeons 
JLibvavp 


1 


Dr.  Clay  Ray  Murray 


MANUAL  OF  ANATOMY. 


MANUAL 


OF 


Practical  Anatomy 


BY 

D.  J.  CUNNINGHAM, 

M  D.  (EDIN.  RT  DUBL.).  D.SC,  I.L.D.   (ST.  AND.  ET  GI.AS.),   D.C.L.   (OXON.),  F.R.S., 
PROFESSOR  OF  ANATOMY  IX    THE    UNIVERSITY  OF  EDINBURGH 


VOLUME  SECOND 
THORAX;  HEAD  AND  NECK 


FOURTH      EDITION 


ILLUSTRATED  WITH  236  EXGRAVIXGS,  MANY  IX  COLORS 


NEW   YORK 

WILLIAM    WOOD   AND    COMPANY 

MDCCCCVII 


CI  i 


All  rights  reserved 


PRINTED    IX    EDINBURGH,    SCOTLAND 


J 


CONTENTS. 


THORAX. 

PAGE 

Introductory,        .......           i 

Thoracic  Wall,    .            .            . 

3 

Thoracic  Cavity,  . 

10 

Mediastinal  Space, 

23 

The  Lungs, 

25 

The  Pericardium, 

35 

The  Heart, 

40 

The  Aorta, 

67 

Trachea,     .... 

78 

Bronchi, 

79 

Thoracic  Duct,     . 

■         87 

Thoracic  Wall,    . 

93 

Thoracic  Joints,   . 

97 

HEAD  AND  NECK. 


Scalp, 

Removal  of  the  Brain,  . 

Dorsal  Aspect  of  the  Trunk. 
Side  of  i  he  Neck, 
Middle  Line  of  the  Neck, 
Dissection-  of  the  Face, 
Temporal  and  Pterygo-Maxillary  Regions, 

v 


104 
1 12 

!32 

17.S 
205 

243 
279 


VI 


I  I  »N1  ENTS 


MAXILLARY    i 

Deep  Dissection  of  the  Neck, 

The  Lateral  Part  of  the  Middle  Craniai    1 

»f  the  Orbit. 
Prevertebral  Region, 
The  Joints  of  the  N 
Mouth  and  Pharynx. 
Carotid  Canal. 

-ior  Maxillary  Nerve, 
Otic  Ganglion. 
Nasal] 

SPHENO  -  PaLATIN  E      (  i  ANGLION 

Artej    . 

Intrapi  rHE    i  altai    Nerve   and  the 

tory  Nerv;  ..... 

The  Lary:  ...... 

Th-                e,  ..... 


and     Internal 


•  295 

■ 

306 

. 

• 

33° 

353 

362 

382 

383 

386 

39i 

Maxillary 

401 

404 
408 

431 


THK  BRAIN, 


General  Appearance  of  the  Brain. 
Membranes  and  Blood- 
Base  of  Brain, 
The  Cerebrum, 
General  Structure  of   jhe  Cerebral  Hemisphei 
Cerebral  Lobes  and  Interlobar  Fissures.    . 
The  Corpus  Callosum.    .... 
Lateral  Ventricle,         .... 
Septum  Lucidum — Fornix — Velum  Interposii  lm. 
Optic  Thalami  and  the  Third  Ventricli 
The  Mesencephalon,       .... 
Basal  Ganglia  of  tt^e  Cerebral  Hemispheri 
Medulla  Oblongata. 
Pons  Varolii, 
Cerebellum, 
Cerebellar  Peduncle- 
Fourth  Ventricle, 


439 

441 

454 
461 

463 
465 
4S2 
487 
497 
502 

507 
514 
521 
533 
533 
540 

54i 


CONTENTS 


VI 1 


THE  AUDITORY  APPARATUS. 


PAGE 

The  External  Ear,         ...                                    .       547 

The  Tympanic  Cavity,     . 

550 

Membrana  Tympani, 

553 

Auditory  Ossicles, 

555 

Eustachian  Tube, 

558 

Vestibule,  .... 

559 

Semicircular  Canals, 

560 

The  Cochlea, 

560 

THE  EYEBALL. 


General  Structure, 

564 

The  Sclerotic, 

565 

The  Cornea, 

566 

The  Vascular  Tunic, 

567 

The  Retina, 

572 

The  Vitreous  Body, 

573 

Crystalline  Lens, 

575 

Chambers  of  the  Eyeball, 

576 

INDEX, 


579 


vol.  11. — a  2 


LIST    OF    ILLUSTRATIONS. 


FIG.  PAGE 

1.  Cervical  Domes  of  the  Pleural  Sacs,  and  parts  in  relation  to 

them,                .......  2 

2.  Diagram  of  one  of  the  Upper  Intercostal  Nerves,            .             .  5 

3.  Dissection  of  the  Anterior  Wall  of  the  Thorax  from  behind,       .  8 

4.  Lines  along  which  the  Sternum  should  be  divided,         .              .  12 

5.  Diagrammatic  representation  of  a  cross  section  through  the  two 

Pleural  Sacs,  .  .  .  .  .  .14 

6.  The  Right  Pleural  Chamber  opened  up  by  the  removal  of  its 

outer  wall,       .  .  .  .  .  <  .15 

7.  The   Left  Pleural  Chamber  opened   up  by  the  removal  of  its 

outer  wall,       .......         17 

8.  Diagram  to  show  the  relation  of  the  lungs  and  the  pleural  sacs 

to  the  anterior  thoracic  wall,  .  .  .  .18 

9.  Diagram  to  show  the  parts  which  lie  in  front  of  the  pericardium 

and  heart,        .......  19 

10.  Left  Pleural  Sac,  ......         20 

11.  Right  Pleural  Sac,  .  .  .  .  .  .21 

12.  Dissection  to  show  the  relations  of  the  Pleural  Sacs  posteriorly,         22 

13.  The  Trachea,  Bronchi,  and  Lungs  of  a  Child,     .  .  .25 

14.  Cervical  Domes  of  the  Pleural  .Sacs,  and  parts  in  relation  to 

them,  .......  26 

15.  The  Mediastinal  Surface  of  a  Right  Lung,  .  .  .27 

16.  Inner  or  Mediastinal  Aspect  of  a  Left  Lung,       .  .  .28 

17.  The  two  Pulmonary  Roots  transversely  divided  close  to  the  hilum 

of  each  lung,   .......  33 

18.  The  Pericardium  and  Great  Vessels  of  the  Heart,  .  .  36 

19.  To  show  position  of  the  Heart  in  relation  to  the  mesial  plane,  .  41 

20.  The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 

Thoracic  Wall.     (Young  and  Robinson),    .  .  .42 

21.  Anterior  or  Sternal  Aspect  of  the  Heart,  .  .  .43 

22.  The  Anterior  Aspect  of  the  Auricular  Part  of  the  Heart,  .         44 

23.  Transverse  section  through  the  Auricular  Part  of  the  Heart  of 

an  Ox,  .......         45 

24.  Posterior  or  Basal  Aspect  of  a  Heart,     .  .  .46 

ix 


x  LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

25.  The  Base  of  the  Ventricular  Part  of  the  Heart,  .  .         47 

26.  The  Coronary   System  of  Veins  on  the  Surface  of  the  Heart. 

(Diagram),      .......  50 

27.  A  portion  of  the  Right  Auricle  of  the  Heart,      .  .  .52 

28.  Sagittal  section  through  the  Right  Auricle  of  the  Heart  and  the 

Root  of  the  Right  Lung.  .  .  .  .  -53 

29.  Interior  of  Right  Auricle  of  Heart,  .  .  .  .54 

30.  Transverse  section  through  the  Ventricular  Part  of  the  Heart. 

(From  Luschka),       ......         56 

31.  The  Interior  of  the  Right  Ventricle,        .  .  .  -57 

32.  Diagram  of  the  arrangement  of  the  Cusps  and  Chordae  Tendinese 

of  the  Tricuspid  Valve,  .  .  .  .  .58 

33.  Heart  of  a  seven  months' Foetus.     (From  Gegenbaur),  .          59 

34.  Dissection  of  a  Heart  to  show  the  Left  Auricle  and  the  Left 

Ventricle.     (Stiles),  .  .  .  .  .61 

35.  Section  through  the  Ventricular  Portion  of  the  Heart,    .  .         62 

36.  Diagram  of  the  arrangement  of  the  Cusps  and  Chordse  Tendineae 

of  the  Mitral  Valve,    ......         63 

37.  The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 

Thoracic  Wall.     (Young  and  Robinson),    .  .  .66 

38.  Transverse  section  through  the  Superior  Mediastinum,  .  .         68 

39.  Transverse  section  through  the  Mediastinal  Space,         .  .         69 

40.  Transverse  section  through  the  Superior  Mediastinum,  .  .         71 

41.  Dissection  of  the  Heart  of  a  Calf  by  Dr.  Waterston  to  show  the 

Auriculo-ventricular  Bundle,  .  .  .  .  -77 

42.  Diagram  of  the  Base  of  the  Ventricular  Portion  of  the  Heart,    .         78 

43.  The  Trachea  and  Bronchi,  .  .  .  .  -79 

44.  Tracing  of  section  through  the  Posterior  Mediastinum,  .         81 

45.  Tracing  of  a  section  through  the  lower  part  of  the  Posterior 

Mediastinum,  ......         82 

46.  Posterior  Aspect  of  the  Heart  with  the  Descending  Aorta,  the 

Trachea  and  Bronchi,  and  the  (Esophagus,    .  .  .83 

47.  The  Thoracic  Duct  and  its  Tributaries.  .  .  .88 

48.  Schema  of  the  Branching  of  the  Two  Bronchi.       From  Gegen- 

baur), .......         91 

49.  Costo-vertebral  Joints  as  seen  from  the  front,     .  .  .99 

50.  Posterior  Common  Ligament  of  the  Vertebral  Column,  .        102 

51.  Section  through  the  Scalp  and  Cranial  Wall,      .  .  .        105 

52.  Superficial  Nerves  on  the  Side  of  the  Neck  and  Back  of  the 

Scalp.     (Hirschfeld  and  Leveillej,          .  .  .        108 

53.  Diagrammatic    section    through    the    Meninges   of    the    Brain. 

(Schwalbe),  .  .  .  .  .  .113 

54.  Mesial  section  through  the  Frontal  Bone  and  corresponding  part 

of  the  Longitudinal  Blood  Sinus,         .  .  .  .115 

55.  Diagram  of  a  coronal  section  through  the  middle  portion  of  the 

cranial  vault  and  subjacent  brain  to  show  the  membranes 

of  the  brain  and  the  Pacchionian  bodies,         .  .  .116 


LIST  OF  ILLUSTRATIONS  xi 

FIG.  PAGE 

56.  The  Dura  Mater  and  the  Superior  Longitudinal  Sinus,  etc.,        .        117 

57.  Sagittal  section  through  the  Skull,  .  .  .  11S 

58.  Coronal  section  through  the  Cranial  Cavity,        .  .  .123 

59.  Aperture   between    the   Dorsum   Sellre   and    the  anterior   con- 

cave  free   margin   of  the    Tentorium.       (Hirschfeld    and 
Leveille),     .  .  .  .  .  .  .124 

60.  Floor  of  the  Cranium,     ......        125 

61.  Pituitary  body.     (Schwalbe),   .  .  .  .  .131 

62.  Skin  incisions  for  the  dissection  of  the  dorsal  aspect  of  the  trunk,        133 

63.  Superficial  dissection  of  the  Back  of  the  Neck,   .  .  .        135 

64.  Diagram  to  show  the  Connexions  of  the  Lumbar  Fascia,  .        141 

65.  Dissection  of  the   Ligamentum   Nucha?  and  of  the    Vertebral 

Artery7  in  the  Neck,     .  .  .  .  .  .147 

66.  Dissection  of  the  Sub-occipital  Region,    .  .  .  155 

67.  Membranes  of  the  Spinal  Cord,  and  the  mode  of  origin  of  the 

Spinal  Nerves,  .  .  .  .  .  .161 

68.  Lateral  view  of  the  Spinal  Cord,  Dura  Mater,  and  Ligamentum 

Denticulatum.     (Hirschfeld  and  Leveille),         .  .       164 

69.  Sagittal  section  through  the  lower  part  of  the  Vertebral  Canal,        165 

70.  A  segment  of  the  spinal  cord  ;  anterior  aspect.      (SCHWALBE, 

after  Allen  Thomson),         .  .  .  .  .167 

71.  Sacral  Canal  opened  up  from  behind.      (After  TESTUT),  .        168 

72.  Transverse    section   through    the   upper   part   of  the   Cervical 

Region  of  the  Cord,     .  .  .  .  .  .172 

73.  Transverse  sections  through  the  Cord  in  different  regions,  .        175 

74.  Transverse  section  through  the  upper  cervical  part  of  the  Cord.         176 

75.  Skin  incisions  for  dissection  of  the  Triangles  of  the  Neck,  .        179 

76.  Superficial  Nerves  on  the  Side  of  the  Neck  and   Back  of  the 

Scalp.     (Hirschfeld  and  Leveille),         .  .  .       1S3 

jy.   Diagrammatic  representation  of  a  transverse  section  through  the 

neck.     (Treves),       .  .  .  .  .  .184 

78.  Dissection  of  the  Posterior  Triangle  of  the  Neck,  .  .        190 

79.  Diagram  of  the  Brachial  Plexus,  ....        194 

80.  Diagram  to  show  the  Boundaries  of  the  Triangles  of  the  Neck,         199 

81.  Dissection  of  the  Front  of  the  Neck,       ....       206 

82.  Sterno-clavicular  and  Costo-sternal  Joints,  .  .  .212 
S3.   Dissection  of  the  Posterior  Triangle  <>f  the  Neck,             .  .        215 

84.  Muscle-Attachments  to  the  Upper  Surface  of  the  First  Rib,  and 

the  Outer  Surface  of  the  Second  Rib,  .  .  .  217 

85.  Diagram  of  the  Subclavian  Artery  and  its  Branches.    (TURNER),  218 

86.  Deep  Dissection  of  the  Root  of  the  Neck  on  the  Left  Side,        .  225 

87.  Diagram  of  the  Cervical  Plexus  and  the  Ansa  Hypoglossi,         .  227 

88.  Transverse  section  through  the  Neck  at  the  level  of  upper  part 

of  Thyroid  Cartilage,  .  .  •  •  231 

89.  Transverse  section  through  the  Neck  at  the  level  of  the  Cricoid 

Cartilage,       .......        232 

90.  Diagram  of  the  Fxternal  Carotid  Artery  and  its  Branches,  .        234 


xii  LIST  OF  ILLUSTRATIONS 

FIO.                                                                                                                                                                              .  PAGE 

91.  Dissection  of  the  Front  of  the  Neck,      ....  241 

92.  Transverse  section  through  the  Thyroid  Body,  Trachea,  and 

Gullet,  at  the  level  of  the  first  Dorsal  Vertebra,        .              .  242 

93.  Eyelid  slightly  everted  to  show  the  Conjunctiva,           .              .  244 

94.  Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands,  247 

95.  Transverse  section  through  the  Head  at  the  level  of  the  I  lard 

Palate,           .......  24S 

96.  Dissection  of  the  Parotid   Region  and  the  upper  part   of  the 

Anterior  Triangle  of  the  Neck,           ....  250 

97.  The  Facial  Muscles,      ......  255 

98.  Arrangement  of  the  Fibres  of  the   Buccinator  Muscle  at   the 

Angles  of  the  Mouth,              .....  257 

99.  Diagram  of  the  Orbicularis  Oris  Muscle,            .              .              .  258 

100.  Nerves  of  the  Face,        ......  262 

101.  Arteries  of  the  Face,      ......  267 

102.  The  Pinna,         .......  269 

103.  Eyelid  slightly  everted  to  show  the  Conjunctiva.            .              .  273 

104.  Diagram  of  the  Structure  of  the  Eyelids,            .              .              .  274 

105.  Dissection  of  the  Right  Eyelid,              ....  275 

106.  Diagram  of  the  Lachrymal  Ducts  and  Sac,  and  of  the  Nasal 

Duct.     (Gegenbaur),          .....  277 

107.  Cartilages  of  the  Nose,                .  279 

108.  Dissection  of  the  Pterygo- maxillary  Space,        .             .             .  283 

109.  Section  through  Temporo-maxillary  Joint,         .              .              .  288 
no.   Diagram  of  the  different  positions  occupied  by  the  head  of  the 

mandible  and  the  interarticular  cartilage  as  the  mouth   is 

opened  and  closed,    ......  289 

111.  Diagram  of  the  C.asserian  Ganglion  and  the  Inferior  Maxillary 

Division  of  the  Fifth  or  Trigeminal  Nerve,                 .              .  291 

112.  Dissection  of  Submaxillary  Region,        ....  297 

113.  Coronal  section  through  the  Tongue  and  Submaxillary  Region 

in  a  plane  behind  the  molar  teeth,     ....  29S 

1 14.  Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands,  299 

115.  Coronal  section  through  the  Closed  Mouth  in  the  plane  of  the 

second  molar  teeth    ......  300 

116.  Diagram  of  Carotid  System  of  Vessels  in  the  Neck  with  the 

Glosso- pharyngeal,   Vagus,   Spinal   Accessory,    and    Hypo- 
glossal Nerves,           ......  308 

117.  Diagram  of  the  relation  of  parts  in  the  Jugular  foramen,           .  311 

118.  Section  through  the  Head  a  little  to  the  right  of  the   .Mesial 

Plane,  .  .  .  .  .  .  .312 

119.  Section    through    the    Cavernous    Sinus.       (After    MERKEL, 

somewhat  modified),               .              .              .              .              .  •  324 
j 20.  Coronal  section  through  the  Cavernous  Sinus  to  show  the  posi- 
tion of  the  Nerves  on  its  wall,            ....  325 

121.  Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa,              .  326 

122.  The  Ophthalmic  Nerve  of  the  Left  Side,           .             .             .  332 


LIST  OF  ILLUSTRATIONS  xiii 

FIf;-  PAGE 

125.   Diagram  of  the  Superior  Oblique  Muscle.     (From  Hermann 

Meyer),  335 

124.  Dissection   of  the    Eyeball   showing    the    Distribution    of  the 

Ciliary  Nerves  and  Vessels,  ....        339 

125.  Diagram  of  the  Ophthalmic  Artery  and  its  Branches.      (After 

Quain  and  Meyer,  modified),         ....  340 

126.  Diagram  of  the  Orbital  Cavity,  .  .  .  342 

127.  Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa,  .  344 

128.  Dissection  of  the  Capsule  of  Tenon  from  the  front,       .  .  346 

129.  Prevertebral  Muscles  of  the  Neck.      (Paterson),         .  .  350 

130.  Dissection  of  the  Ligamentum  Nucha?  and   of  the  Vertebral 

Artery  in  the  Neck,  .....        352 

131.  Coronal    section    through    bodies    of  certain    of  the    Cervical 

Vertebrae,      ........        354 

132.  The  Ligamenta  Subflava  in  the  Lumbar  Region  of  Spine,        .       356 

133.  Mesial  section  through  the  Basilar  Process  of  Occipital  Bone, 

the    Atlas,     and    the     Axis.     (From     Luschka,     slightly 
modified),       .......        358 

134.  Dissection  from  behind  of  Ligaments  connecting  the  Occipital 

Bone,  the  Atlas,  and  the  Axis  with  each  other,         .  .  360 

135.  The  Sublingual  Region  in  the  Interior  of  the  Mouth,    .  .  364 

136.  Isthmus  of  the  Fauces  as  seen  through  the  widely  opened  Mouth,  365 

137.  Profile  view  of  the  Pharynx  to  show  the  Constrictor  Muscles. 

(From  Turner),       ......       369 

138.  Sagittal   section    through    the    Nasal    Chamber,    the    Mouth, 

Larynx,  and  Pharynx,    a  little   to  the  right  of  the  mesial 
plane,  .......        372 

139.  Superior    Aperture    of  Larynx    exposed    by    laying    open    the 

pharynx  from  behind,  .....        375 

140.  Transverse  section  through  the  Neck  at  the  level  of  upper  part 

of  Thyroid  Cartilage,    .  .  .  .  .       376 

141.  Diagram  of  the  Superior  Maxillary  Nerve, 

142.  Antero- posterior    section    through    the    Nose,     Mouth,     and 

Pharynx,  a  little  to  the  left  of  the  mesial  plane,         .  .        388 

143.  Coronal    section    through    the    Nasal    Cavities    opposite    the 

Crista  Galli  of  the  Ethmoid  Bone,     ....  392 

144.  Outer  Wall  of  the  Left  Nasal  Fossa.      (From  SCHWALBE),       .  394 

145.  Outer  Wall  of  Nasal  Chamber  and  Naso-pharynx,        .  .  396 

146.  Diagram  of  the  Facial  Nerve.      (Thane,  Quairis  Anatomy),  406 

147.  Coronal  section  through  Larynx  to  show  Compartments,  .  410 

148.  The    Larynx    as    seen    in  the  living  person  by  means  of  the 

laryngoscope,  .  .  .  .  .  .411 

149.  Mesial  section  through    Larynx  to  show  the  Outer  Wall  of  the 

Right  Half,    .......  412 

150.  Diagram  of  Rima  Glottidis,       .....  413 

151.  The  Crico-thyroid  Muscle,         .....  4I0 

152.  Muscles  on  the  Posterior  Aspect  of  the  Larynx,  .  .  417 


j< 


XIV 

FIG. 

153- 

154- 
155- 

156. 

157. 
158. 

159- 

160. 

161. 
162. 

163. 
164. 

165. 


166. 

167. 

168. 
169. 

170. 
171. 
172. 

173- 

174. 

175- 

176. 

177. 

178. 
179. 

180. 

181. 
182. 

183. 
184. 


LIST  OF  ILLUSTRATIONS 

PAGE 

Muscles  in  the  Lateral  Wall  of  Larynx,            .             .             .  419 
Lateral  part  of  Cricothyroid  Membrane,           .              .              .421 

Cartilages  and  Ligaments  of  Larynx  viewed  from  the  front,      .  426 

Profile  view  of  Cartilages  and  Ligaments  of  Larynx,    .              .  427 

Cartilages  and  Ligaments  of  Larynx  as  viewed  from  behind,   .  428 

The  Sublingual  Region  in  the  Interior  of  the  Mouth,  .             .  433 

Muscles  of  the  Tongue.     (From  Gegenbaur),              .             .  435 
Transverse   section    through   the  hinder  part  of  the  Tongue. 

(From  Gegenbaur),            .....  436 

Longitudinal  section  through  the  Tongue.     (From  Aeby),       .  437 

Transverse  section  through  the  Tongue.     (From  Aeby),          .  438 

The  Base  of  the  Brain  with  the  Cranial  Nerves  attached,         .  440 
Diagrammatic   section    through   the    Meninges  of  the  Brain. 

(Schwalbe),             ......  442 

Diagram  of  a  coronal  section  through  the  middle  portion  of 
the   cranial   vault  and  subjacent  brain  to  show  the  mem- 
branes of  the  brain  and  the  Pacchionian  bodies,      .              .  443 
Floor  of  the  Cranium  after  the  removal  of  the  Brain  and  the 

Tentorium  Cerebelli,              .....  446 

Internal   and   Tentorial   Surfaces  of  the   left  Cerebral  Hemi- 
sphere.    (Semi-diagrammatic),         ....  448 

Inferior  Surface  of  the  Cerebral  Hemisphere,                .             .  450 
Outer  Surface  of  the  Cerebral  Hemisphere.     (Semi-diagram- 
matic),            .             .             •             •             •             •             •  451 

Diagram  of  the  Circle  of  Willis,  .  .  .  .453 

The  Base  of  the  Brain  with  the  Cranial  Nerves  attached,          .  455 
Front  view  of  the   Medulla,   Pons,  and  Mesencephalon  of  a 

full-time  Foetus,         ......  457 

Section  through  the  Head  a  little  to  the  right  of  the  Mesial 

Plane,            .......  459 

Diagrammatic  view  of  the  manner  in  which  the  several  parts  of 

the  Brain  are  connected  with  each  other.  (From  Schwalbe),  460 

Gyri  and  Sulci  on  the  Outer  Surface  of  the  Cerebral  Hemisphere,  464 
The  Gyri  and  Sulci   on   the  Mesial  Aspect  of  the   Cerebral 

Hemisphere,              ......  468 

Gyri  and  Sulci  on  the  Tentorial  and  Orbital  Surfaces  of  the 

Cerebral  Hemispheres,  .  .  .  .  .471 

Posterior  Part  of  Inner  Surface  of  the  Left  Hemisphere,          .  477 
Fissures   and    Gyri    on    the    Surface  of  the   Insula.     (Eber- 

staller),     .....••  479 

The  Corpus  Callosum  exposed  from  above  and  the  Right  Half 

dissected  to  show  the  course  taken  by  the  Fibres,     .             .  484 

Mesial  section  through  the  Brain,          ....  485 

Anterior   end    of  the    Corpus    Callosum    and    its    Peduncles. 

(From  Cruveilhier),          .....  486 

Dissection  to  show  the  Lateral  Ventricles,        .             .             .  487 

Cast  of  the  Ventricles  of  the  Brain.     (From  Retzius),             .  488 


LIST  OF   ILLUSTRATIONS  xv 


FIG. 


185.  Dissection  to  show  the  Posterior  and  Descending  Cornua  of 

the  Lateral  Ventricle  on  the  left  side,  .  .  .        489 

186.  Coronal  section  through  the  Cerebrum,  .  .  .       490 

187.  Coronal  section  through  the  Posterior    Horns  of  the  Lateral 

Ventricles,    ...  ....       492 

188.  Dissection  to  show  the  Posterior  and  Descending  Cornua  of 

the  Lateral  Ventricle,  .....       494 

189.  Coronal  section  through  the  Cerebrum,  Mid-brain,  and  Pons 

Varolii  in  the  plane  of  the  geniculate  bodies,  .  .       495 

190.  Diagram  of  the  Fornix  ;  profile  view,  .  .  •       499 

191.  Dissection  to  show  Velum  Interpositum  and  the  parts  in  its 

vicinity,         .......        500 

192.  Diagrammatic  coronal  section  through  the  Optic  Thalami  and 

the  parts  in  immediate  relation  to  them,        .  .  .501 

193.  The  two  Optic  Thalami  and  the  Third  Ventricle  as  seen  from 

above,  .......        503 

194.  Mesial  section  through  the  Corpus  Callosum,  Third  Ventricle, 

Mesencephalon,  Pons,  Cerebellum,  and  Medulla,     .  .        506 

195.  Diagrammatic  outline  of  the  Third  Ventricle  as  viewed  from 

the  side,         .......        507 

196.  Diagram  of  the  Roots  of  the  Optic  Tract,  .  .  .        509 

197.  The  Origin  and   Relations  of  the    Optic    Tract.       (Professor 

Thane,  from  Quairfs  Anatomy),      .  .  .  .510 

198.  Diagrammatic  view  of  the  Cut  Surface  of  the  Mesencephalon 

when  transversely  divided,    .  .  .  .  .511 

199.  Transverse  section  through  the  Mesencephalon  at  the  level  of 

the  inferior  quadrigeminal  body,       .  .  .  .512 

200.  Section    through   upper    part   of  Mesencephalon    at    level    of 

superior  quadrigeminal  body,  .  .  .  5 1 3 

201.  Horizontal  section  through  the  Right  Cerebral  Hemisphere  at 

the  level  of  the  widest  part  of  the  lenticular  nucleus,  .        515 

202.  Coronal  section  through  the  Frontal  Lobes  of  the  Cerebrum,  .       516 

203.  Coronal  section  through  the  Cerebrum  so  as  to  cut  through  the 

anterior  part  (putamen)  of  the  lenticular  nucleus,     .  •        5J7 

204.  Coronal  section  through  the  Cerebrum  in  such  a  plane  as  to 

cut  the  three  parts  of  the  lenticular  nucleus,  .  •        518 

205.  Front  view  of  the  Medulla,  Pons,  and  Mesencephalon  of  a  full- 

time  Foetus,  .  .  .  .  .  .521 

206.  Diagram  of  the  Decussation  of  the  Pyramids.      (Modified  from 

Van  Gehuchten),  .  .  .       523 

207.  Lateral  view  of  the  Medulla.  Pons,  and  Mesencephalon  of  a 

full-time  Foetus,         ......        524 

208.  Back  view  of  the  Medulla,  Pons,  and  Mesencephalon  of  a  full- 

time  Foetus,  ......        526 

209.  Section  through  the  lower  part  of  the  Medulla  of  the  Orang,    .       529 

210.  Transverse  section  through  the  closed  part  of  the  Medulla  of  a 

full-time  Foetus,         ......       530 


xvi  LIST  OF  ILLUSTRATIONS 


FIG. 


211.  Transverse  section  through  lower  end  of  the  Medulla  of  a  full- 

time  Foetus,               ......  530 

212.  Transverse  section  through  the  Medulla  of  newd:>orn  Child,     .  531 

213.  Transverse  section  through  the  Medulla,            .              .              .  532 

214.  Upper  Surface  of  the  Cerebellum,         ....  536 

215.  Lower  Surface  of  the  Cerebellum,         ....  537 

216.  Mesial    section    through     the    Vermis     of    the    Cerebellum. 

(From  Gegenbaur),             .....  538 

217.  Transverse  section  through  the  upper  part  of  the  Pons  Varolii  of 

the  Orang,     .......  545 

218.  Coronal  section  of  the  Right  Temporal  Bone,  .              .              .  548 

219.  Vertical      transverse      section      through      the      Right       Ear. 

(HOWDEN),    .......  549 

220.  Schematic  vertical  section  through    the   Tympanum.      (From 

Testut),       .  .  .  .  .  .  -550 

221.  Section  through  the  Left  Temporal  Bone  showing  the  Inner 

Wall  of  the  Tympanic  Cavity.      (Howdex),  .  551 

222.  Left  Membrana  Tympani  and  Recessus  Epitympanicus  viewed 

from  within.     (Howdex),    .....        552 

223.  Left  Membrana  Tympani  and  Chain  of  Tympanic  Ossicles  seen 

from  the  inner  aspect.     (Howdex),  .  .  .       553 

224.  Left    Tympanic    Membrane    as    viewed    from     the     external 

auditory      meatus      during      an      otoscopic      examination. 

(Howdex ),  .......  554 

225.  Left  Malleus  and  Incus.     (Helmholtz),  .  .  .  555 

226.  The  Left  Malleus.     (Howdex),  ....  556 

227.  The  Left  Incus.     (Howdex),  .....  556 

228.  Left  Stapes.     (Howdex),         .....  557 

229.  Interior  of  the  Left  Bony  Labyrinth  viewed  from  the   outer 

aspect.     (Howdex  1.  .....       559 

230.  Left  Bony  Labyrinth  viewed  from  outer  side.      (Howdex ),     .        560 

231.  Diagram  of  the  Osseous  and  Membranous  Labyrinth.     (Modi- 

fied  from  Testut),  .....       562 

232.  Horizontal  section  through  the  Left  Eyeball.      (Diagrammatic),        564 
255.   Diagram    of    the    posterior    aspect    of     the     Left     Eyeball. 

(After  Testut,  modified),         .  ....       566 

234.  Dissection  of  the  Eyeball  showing  the  Vascular  Tunic  and  the 

Distribution  of  the  Ciliary  Nerves  and  Vessels.         .  .        568 

235.  The   Ciliary  Processes   of  the  Human   Eyeball    viewed   from 

behind.      (MERKEL),  .....        569 

236.  Diagrammatic  representation  of  the  Ciliary  Region,  as  seen  in 

vertical  section,  ......        574 


MANUAL    OF    ANATOMY. 


MANUAL 

OF 

PRACTICAL    ANATOMY. 

THORAX. 

THE  dissection  of  the  thorax  is  commenced  on  the  eleventh 
day1  after  the  subject  has  been  placed  in  the  dissecting- 
room.  By  this  time  the  upper  limbs  have  been  detached 
from  the  trunk. 

In  form  the  thorax  resembles  a  truncated  cone.  In  front 
and  behind  it  is  flattened  ;  but  laterally  it  is  full  and  rounded. 
During  life  the  movements  of  the  thoracic  walls  produce 
alterations  in  the  capacity  of  the  Chest  cavity,  and  play  an 
essential  part  in  the  function  of  respiration. 

In  front,  the  thoracic  cavity  is  bounded  by  the  sternum 
and  costal  cartilages ;  behind,  it  is  bounded  by  the  twelve 
dorsal  vertebrae  and  the  intervening  cartilaginous  discs, 
together  with  the  portions  of  the  ribs  which  extend  outwards 
from  the  vertebral  column  as  far  as  the  angles ;  laterally,  the 
shafts  of  the  ribs,  from  their  angles  behind  to  their  anterior 
extremities  in  front,  limit  the  thoracic  cavity.  These  parts 
constitute  the  framework  of  the  thorax,  and  can  be  studied  on 
the  skeleton. 

The  anterior  wall  of  the  thorax  is  shorter  than  the  posterior 
wall.  Thus,  during  expiration,  the  upper  margin  of  the 
manubrium  sterni   is  placed   opposite   the  disc  between  the 


1  Saturdays  and  Sundays  are  not  counted. 
VOL.  II  —  1 


THORAX 

second  and  third  dorsal  vertebrae,  whilst  the  lower  end  of  the 
body  of  the  sternum  corresponds  in  level  with  the  middle 
point  of  the  body  of  the  ninth  dorsal  vertebra.  The  bodies 
of  the  dorsal  vertebrae  project  forwards  into  the  cavity  of  the 
thorax,  and  greatly  diminish  its  antero-posterior  diameter  in 
the  mesial  plane  ;  but  on  either  side  of  the  vertebral  column, 
owing  to  the  backward  sweep  of  the  posterior  portions  of  the 
ribs,  a  deep  hollow  is  formed  for  the  reception  of  the  most 
massive  part  of  the  lung. 

The  superior  aperture,   or  inlet  of  the  tliorax,  is  a  narrow 
opening  which  is  bounded  by  the  first  dorsal  vertebra,   the 


subclavian  artery 

Righl 
innominate  vein 


Innominate 
artery 


Trachea 
Vagus  nerve  \ 

Right 


<  Ksophagus 


Left  subclavian  artery 
Sulcus  subclavius 


VagUS  nerve 


Left 

common 

carotid 

Left 

nnominate 

vein 


FiG.  i. — Cervical  Domes  of  the  Pleural  Sacs,  and  parts  in  relation  to  them. 


fust  pair  of  costal  arches,  and  the  manubrium  sterni.  The 
plane  of  this  opening  is  very  oblique ;  it  slopes  from  behind 
forwards  and  downwards.  Through  the  inlet  of  the  thorax 
the  apices  of  the  lungs  project  upwards  into  the  root  of  the 
neck,  and  between  these  the  windpipe,  gullet,  the  pneumo- 
gastric  nerves,  the  gangliated  cords  of  the  sympathetic,  and 
the  great  veins  which  carry  blood  towards  the  heart  from  the 
head  and  neck  and  the  superior  extremities  enter  the  chest; 
through  the  same  opening  egress  is  given  to  the  thoracic  duct 
and  to  the  arteries  which  convey  blood  to  the  neck,  head, 
and  upper  limbs. 

The  base  or  dependent  part  o(  the  thorax  is  very  wide, 
and  is  sometimes  called  the  outlet.  In  front  it  is  bounded 
by  the  ensiform  cartilage,  and  behind  by  the  twelfth  dorsal 
vertebra.  Between  these  points  the  lower  margin  of  the 
thorax  presents  a  curved  outline.      Starting  from  the  sternum, 


THORACIC  WALL  3 

it  proceeds  downwards,  outwards,  and  backwards  along  the 
cartilages  of  the  seventh,  eighth,  ninth,  and  tenth  ribs.  At 
the  tip  of  the  eleventh  rib  the  direction  of  the  lower  margin 
of  the  thorax  changes,  and  it  proceeds  upwards,  backwards, 
and  inwards  along  the  twelfth  rib  to  the  vertebral  column. 

Attached  to  the  lower  margin  of  the  thorax  is  the  dia- 
phragm, a  muscular  partition  which  intervenes  between  the 
cavity  of  the  chest  above  and  the  cavity  of  the  abdomen 
below.  It  is  highly  vaulted  or  dome-shaped,  and  projects 
upwards  so  as  to  form  a  convex  floor  for  the  thorax,  and  a 
concave  roof  for  the  abdomen.  The  upward  projection  of 
the  diaphragm  greatly  diminishes  the  vertical  depth  of  the 
thoracic  cavity. 

But  the  diaphragm  does  not  form  an  unbroken  partition. 
It  presents  three  large  openings,  by  means  of  which  structures 
pass  to  and  from  the  thorax,  viz. — (1)  for  the  aorta,  thoracic 
duct,  and  vena  azygos  major;  (2)  for  the  oesophagus  and 
pneumogastric  nerves  ;  (3)  for  the  inferior  vena  cava.  Besides 
these  there  are  other  smaller  apertures  which  will  be  mentioned 
later  on. 


THORACIC  WALL. 

Two  days  at  least  should  be  devoted  to  the  dissection  of 
the  thoracic  wall. 

In  addition  to  the  osseous  and  cartilaginous  framework, 
the  walls  of  the  chest  are  built  up  partly  by  muscles,  and 
partly  by  membranes,  and  in  connection  with  these  there  are 
numerous  nerves  and  blood-vessels. 


(  External  intercostals. 
\  Int 


Muscles,         .         .  J  Internal  intercostals. 

I  Triangularis  sterni. 

[  Anterior  intercostal  membranes. 
Membranes,  .         .  J  Posterior  intercostal  membranes. 

I  Pleural  membrane  (parietal  part). 

/"Intercostal  nerves. 

XT  i  a  ♦     •         Aortic  intercostal  arteries. 

iScrves  and  Arteries,    e         .  ,  , 

j  Superior  intercostal  artery. 

ternal  mammary  artery. 


Un 


Dissection. — Portions  of  certain  of  the  muscles  of  the  upper  limb  and  of 
the  abdominal  wall  will  be  noticed  attached  to  the  thoracic  wall.  From 
before  backwards  the  dissector  will  meet  with  the  pectoralis  major,  the 
pectoralis  minor,  and  the  serratns  magnus,  whilst  towards  the  lower  margin 
of  the  chest  he  will  recognise  the  rectus  abdominis  in  front,  and  the 
obliquus  externus  and  laiissimns  dorsi  upon  its  lateral  aspect.  The  rounded 
11— 1  a 


4  .  THORAX 

tendon  of  the  subclavins  may  also  be  observed  taking  origin  from  the  first 
costal  arch,  and  posteriorly  to  this  the  scalenus  posticus  extends  downwards 
to  its  insertion  into  the  second  rib.  With  the  single  exception  of  the 
scalenus  posticus,  these  muscles  should  be  removed  so  as  to  lay  bare  the 
costal  arches  and  the  intercostal  muscles.  In  detaching  the  serratus  magnus 
be  careful  not  to  injure  the  lateral  cutaneous  nerves  which  make  their 
appearance  in  the  intervals  between  its  digitations.  The  anterior  cutaneous 
nerves  and  perforating  branches  of  the  internal  mammary  artery  must  also 
be  preserved  ;  they  pierce  the  origin  of  the  pectoralis  major  in  the  intervals 
between  the  costal  cartilages,  and  close  to  the  margin  of  the  sternum. 

Intercostal  Muscles. — These  muscles  occupy  the  eleven 
intercostal  spaces  on  each  side  of  the  thoracic  wall.  In  each 
space  there  are  two  strata  of  muscular  fibres — a  superficial 
and  a  deep.  The  superficial  layer  of  muscular  fibres  is  called 
the  external  intercostal  muscle,  and  the  deep  layer  the  internal 
intercostal  muscle. 

The  external  intercostal  ninscles  (musculi  intercostales  externi) 
are  already  exposed,  and  very  little  cleaning  is  necessary  to 
bring  out  their  connections.  Observe  that  entering  into  their 
constitution  there  is  a  large  admixture  of  tendinous  fibres,  and 
that  these,  as  well  as  the  muscular  fibres,  are  directed  from 
above,  obliquely  downwards  and  forwards  from  the  lower 
border  of  the  rib  above  to  the  upper  border  of  the  rib  below. 
They  do  not  extend  farther  forwards  in  the  various  spaces 
than  a  point  corresponding  to  the  union  of  the  bony  with  the 
cartilaginous  parts  of  the  costal  arches.  In  many  cases, 
especially  in  the  upper  spaces,  they  do  not  reach  so  far. 
Here  the  muscular  fibres  stop  short,  but  the  tendinous  fibres 
are  prolonged  onwards  to  the  sternum  in  the  form  of  a 
membrane,  which  may  be  called  the  anterior  intercostal  mem- 
brane. The  external  intercostal  muscles  of  the  two  lower 
spaces  are  exceptions  to  this  rule.  They  extend  forwards  to 
the  extremities  of  the  spaces.  Posteriorly  the  muscles  pass 
backwards  as  far  as  the  tubercles  of  the  ribs,  but  this  is  a 
point  which  can  only  be  satisfactorily  demonstrated  after  the 
thorax  has  been  opened. 

Dissection. — To  bring  the  internal  intercostal  muscles  into  view  it  is 
necessary  to  reflect  the  external  intercostal  muscles,  and  also  the  anterior 
intercostal  membranes.  Divide  them  along  the  upper  borders  of  the  ribs 
which  bound  the  spaces  inferiorly,  and  throw  them  upwards.  This  dissec- 
tion should"  be  performed  in  each  intercostal  space,  and,  in  effecting  it, 
care  must  be  taken  of  the  intercostal  arteries  which  lie  between  the  two 
muscular  strata. 

The  internal  intercostal  muscles  (musculi  intercostales  interni) 
thus  laid  bare  will  be  seen  to  be  similar  in  their  constitution 


THORACIC  WALL 


TRIANG.  STERNI 


to  the  external  muscles.  The  fibres,  however,  run  in  the 
opposite  direction — viz.,  from  above,  obliquely  downwards  and 
backwards.  Superiorly,  they  are  attached  to  the  inner  surface 
of  the  upper  rib,  immediately  above  the  subcostal  groove ; 
inferiorly,  they  are  attached  upon  the  inner  surface  of  the 
lower  rib,  close  to  the  upper  margin.  The  internal  intercostal 
muscles  are  prolonged  forwards  to  the  sternum.  Posteriorly 
they  reach  backwards  to  the  angles  of  the  ribs,  from  which 
to  the  spine  the  muscles  are  replaced  by  a  series  of  thin 
membranes  —  the  pos- 
terior intercostal  mem- 
branes— which  will  be 
seen  after  the  thorax 
has  been  opened.  If 
the  internal  oblique 
muscle  of  the  abdomen 
has  not  been  removed, 
the  dissector  should 
note  that  the  anterior 
fibres  of  the  two  lowest 
internal  intercostal 
muscles  become  con- 
tinuous with  the  fibres 
of  that  muscle. 

Intercostal  Nerves. 
—  The  intercostal 
nerves  are  altogether 
out  of  sight  in  the 
present  stage  of  the 
dissection.      They   are 

hidden  by  the  lower  borders  of  the  ribs  which  bound  the 
intercostal  spaces  superiorly.  By  gently  pulling  upon  their 
lateral  cutaneous  branches  they  can  be  drawn  downwards, 
and  they  are  then  seen  to  lie  between  the  two  muscular  strata 
as  far  forward  as  a  point  midway  between  the  spine  and 
sternum.  Here  they  disappear  from  view  by  sinking  into 
the  substance  of  the  internal  intercostal  muscles,  amidst  the 
fibres  of  which  they  may  be  traced  as  far  as  the  anterior 
extremities  of  the  bony  ribs.  They  now  reach  the  deep 
surface  of  these  muscles  and  are  carried  inwards,  first  upon 
the  pleura,  and  then  upon  the  triangularis  sterni  muscle. 
Lastly,  they  cross  the   internal   mammary  artery,   and   come 


Fig.  2. — Diagram  of  one  of  the  Upper 
Intercostal  Nerves. 


6  THORAX 

forwards  at  the  side  of  the  sternum  as  the  anterior  cutaneous 
nerves  of  the  pectoral  region.  Each  nerve,  before  it  reaches 
the  surface,  pierces — (a)  the  internal  intercostal  muscle ;  (b) 
the  anterior  intercostal  membrane ;  (c)  the  origin  of  the 
pectoralis  major;  and  (d)  the  deep  fascia  (Fig.  2). 

But  this  description  only  holds  good  for  the  upper  five 
intercostal  nerves.  The  lower  six  nerves,  on  leaving  the 
anterior  ends  of  the  intercostal  spaces,  pass  forwards  into  the 
abdominal  wall  between  the  internal  oblique  and  transversalis 
muscles,  where  they  have  already  been  displayed  by  the 
dissector  of  the  abdomen. 

The  intercostal  nerves,  as  they  traverse  the  thoracic  wall, 
give  off — (a)  the  lateral  cutaneous  branches,  (b)  twigs  to  the 
intercostal  muscles  and  triangularis  sterni.  Their  terminal 
branches  constitute  the  anterior  cutaneous  nerves.  The 
lateral  cutaneous  branches  come  off  midway  between  the  spine 
and  the  sternum,  and,  piercing  the  external  intercostal 
muscles,  appear  in  the  intervals  between  the  digitations  of  the 
serratus  magnus. 

The  first  intercostal  nerve  gives  off  no  lateral  and  no 
anterior  cutaneous  branch  ;  the  lateral  cutaneous  branch  of 
the  second  intercostal  nerve  takes  the  form  of  the  intercosto- 
humeral  nerve. 

It  is  not  necessary  to  make  a  dissection  of  the  intercostal  nerves  in  more 
than  two  or  three  of  the  spaces. 

Intercostal  Vessels. — The  intercostal  arteries  should  be 
dissected  in  those  spaces  in  which  the  nerves  have  not  been 
traced,  and  in  which,  therefore,  the  internal  intercostal 
muscles  are  still  entire.  It  is  only  in  a  well-injected  subject 
that  a  satisfactory  view  of  these  vessels  can  be  obtained.  In 
each  intercostal  space  one  artery  is  found  passing  from  behind 
forwards ;  and  in  each  of  the  upper  nine  intercostal  spaces, 
two,  the  anterior  intercostal  arteries,  running  from  before 
backwards. 

In  the  upper  two  spaces  the  vessels  which  run  from  behind 
forwards  are  derived  from  the  superior  intercostal  branch  (truncus 
costo-cervicalis)  of  the  subclavian  artery  ;  in  the  nine  lower 
spaces  they  spring  directly  from  the  aorta,  and  are  called  the 
aortic  intercostal  arteries. 

The  anterior  intercostal  arteries  of  the  upper  six  spaces 
proceed  directly  from  the  internal  mammary,  whilst  in  the 


THORACIC  WALL  7 

case  of  the  seventh,  eighth,  and  ninth  spaces  they  come  from 
the  outer  of  its  two  terminal  branches — viz.,  the  musculo- 
phrenic artery. 

The  intercostal  vessels  are  for  the  most  part  distributed 
between  the  two  muscular  strata.  From  the  angles  of  the 
ribs  onwards  to  a  point  midway  between  the  spine  and 
sternum,  the  aortic  intercostal  arteries  lie  under  shelter  of  the 
lower  margins  of  the  ribs  which  bound  the  spaces  superiorly, 
and  at  a  higher  level  than  the  corresponding  nerves.  Here 
each  divides  into  two  branches,  and  these  pass  forwards  in 
relation  to  the  upper  and  lower  margins  of  the  intercostal 
space.  They  give  off  small  branches  which  accompany  the 
lateral  cutaneous  nerves.  The  lower  two  aortic  intercostal 
arteries  are  carried  onwards  beyond  the  thoracic  wall  into 
the  abdominal  wall.  The  superior  intercostal  arteries  are  dis- 
posed in  a  manner  similar  to  the  aortic  intercostal  vessels. 

The  anterior  intercostal  arteries  are  two  in  number  for  each 
space.  At  their  origin  they  lie  under  cover  of  the  internal 
intercostal  muscles,  and  they  run  outwards  in  relation  to 
the  upper  and  lower  margins  of  the  ribs  bounding  each 
space.  After  a  short  course  they  pierce  the  internal  inter- 
costal muscles,  and  end  by  anastomosing  with  the  aortic 
and  superior  intercostal  arteries. 

Dissection. — The  dissector  should  next  proceed  to  remove  the  intercostal 
muscles.  This  dissection  must  be  carried  out  with  more  than  usual  care, 
because  immediately  subjacent  to  the  internal  intercostal  muscles,  over  the 
greater  extent  of  the  chest  wall,  is  the  delicate  pleural  membrane  lining  the 
inner  surface  of  the  costal  arches.  Upon  no  account  detach  this  me??ibrane 
from  the  deep  surface  of  the  ribs,  and  take  the  greatest  care  to  preserve  it 
intact  during  the  dissection. 

On  the  front  of  the  chest,  the  internal  mammary  artery  and  the  triangu- 
laris sterni  muscle  will  be  seen  to  intervene  between  the  pleura  and  the 
costal  cartilages.  The  internal  mammary  artery,  with  its  two  companion 
veins,  descends  in  a  vertical  direction,  about  half  an  inch  from  the  outer 
margin  of  the  sternum.  Clean  these  vessels  carefully  in  the  intervals 
between  the  costal  cartilages,  and  note  some  small  lymphatic  glands 
which  lie  along  the  course  of  the  vessels.  As  a  rule,  the  artery  ends 
by  dividing  into  two  terminal  branches  in  the  interval  between  the  sixth 
and  seventh  rib  cartilages.  Most  likely  this  space  will  be  so  narrow 
that  a  view  of  the  bifurcation  cannot  be  obtained.  If  this  be  the  case,  pare 
away  the  edges  of  the  cartilages  over  the  artery,  or  if  necessary  remove  the 
inner  part  of  the  sixth  cartilage  completely.  The  perforating  branches  of 
the  internal  mammary  artery  which  accompany  the  anterior  cutaneous 
nerves  should  be  preserved. 

The   muscle   upon    which    the   internal    mammary   artery    lies   is   the 
triangularis  sterni.      Endeavour  to  define  its  slips  in  the  intervals  between 
the  costal  cartilages. 
11— lb 


8 


THORAX 


Towards  the  lower  margin  of  the  thorax  the  pleural  sac  is  not  prolonged 
downwards  to  the  lowest  limit  of  the  recess  between  the  diaphragm  and 
the  costal  arches.  Indeed,  in  the  axillary  line,  it  will  be  found  to  fall 
considerably  short  of  this.  Consequently,  when  the  internal  intercostal 
muscles  are  removed  from  this  portion  of  the  chest  wall,  the  dissector  will 
come  down  directly  upon  the  diaphragm  ;  and,  as  the  fibres  of  the 
diaphragm  correspond  somewhat  in  their  direction  with  those  of  the 
internal  intercostal  muscles,  it  is  no  uncommon  occurrence  for  the  student 


Sternohyoid  ~-4^^    rj- 
Sterno-thyroid  ~^j£k        jm  ; 

Triangularis  sterni 


Intercostal  nerve 
and  artery 


Internal  mammary 
artery 

Sternal  glands 


Triangularis 
terni 

Musculo- 
phrenic artery 


| 

Musculo-  S^*J 

phrenic 
artery 

Fig.  3. — Dissection  of  the  Anterior  Wall  of  the  Thorax  from  behind. 

to  remove  them,  and  thus  expose  the  peritoneum,  under  the  impression 
that  he  has  simply  laid  bare  the  pleura.  When  the  dissection  has  been 
properly  executed,  a  strong  fascia  will  be  observed  to  pass  from  the  surface 
of  the  diaphragm  on  to  the  surface  of  the  costal  pleura  so  as  to  hold  it  in 
position.     Preserve  this  for  further  examination. 

Internal  Mammary  Artery  (arteria  mammaria  interna). — 
This  vessel  arises  in  the  root  of  the  neck  from  the  first  part  of 
the  subclavian,  and  enters  the  thorax,  by  passing  downwards 
behind  the  inner  end  of  the  clavicle  and  the  cartilage  of  the 


THORACIC  WALL  9 

first  rib.  Accompanied  by  two  veins,  it  descends  to  the 
interval  between  the  sixth  and  seventh  costal  cartilages,  where 
it  ends  by  dividing  into  the  superior  epigastric  and  the  musculo- 
phrenic bra?iches.  It  runs  parallel  with  the  outer  margin  of  the 
sternum,  from  which  it  is  separated  by  an  interval  of  about 
half  an  inch. 

Placed  in  front  of  the  internal  mammary  artery  are  the 
upper  six  costal  cartilages,  with  the  intervening  intercostal 
muscles  and  anterior  intercostal  membranes.  It  is  crossed 
by  the  series  of  intercostal  nerves  before  they  turn  forwards 
to  gain  the  surface.  In  the  upper  part  of  its  course  the 
artery  is  supported  behind  by  the  pleura,  but  lower  down 
it  rests  upon  the  triangularis  sterni,  which  intervenes  between 
it  and  the  pleural  sac. 

In  addition  to  its  two  terminal  branches,  a  large  number 
of  small  collateral  twigs  proceed  from  the  internal  mammary — 

1.  The  anterior  intercostal,  .  \        ,     thoracic  narietes 

2.  The  perforating,  .  J  r 

^.   The  conies  nervi  phrenici,!  ,  .,,...        c  ,1     ,1 

J    ,,   \.    ,.     ,        ,  X       .      '  J- to  parts  in  the  interior  of  the  thorax. 

4.  Mediastinal  and  thymic,  .  J       l 

5.  Superior  epigastric,  .  j   h    terminal  branches. 

6.  Musculo-phrenic,     .         .  J 

The  anterior  intercostal  arteries  (rami  intercostales)  are 
supplied  to  the  upper  six  intercostal  intervals,  and  have 
already  been  dissected  (p.  6).  Two  are  given  to  each  space  : 
frequently  these  arise  by  a  common  trunk. 

The  perforathig  arteries  (rami  perforantes)  accompany  the 
anterior  cutaneous  nerves,  and  reach  the  surface  by  piercing 
the  internal  intercostal  muscles,  the  anterior  intercostal 
membranes,  and  the  pectoralis  major  muscle.  One,  or 
perhaps  two,  are  given  off  in  each  intercostal  space.  And  in 
the  female  two  or  three  of  the  intermediate  members  of  the 
series  (rami  mammarii)  attain  a  special  importance,  inasmuch 
as  they  constitute  the  principal  arteries  of  supply  to  the 
mammary  gland. 

The  superior  epigastric  artery  (arteria  epigastrica  superior) 
enters  the  sheath  of  the  rectus  muscle  of  the  abdominal  wall 
by  passing  downwards  behind  the  seventh  costal  cartilage. 

The  musculo-phrenic  artery  (arteria  musculo-phrenica)  turns 
outwards  and  downwards  along  the  costal  origin  of  the 
diaphragm  and  behind  the  rib-cartilages.  Opposite  the 
eighth  costal  cartilage  it  pierces  the  diaphragm  and  terminates 


io  THORAX 

on  its  abdominal  surface.     It  gives  off  the  anterior  intercostal 
arteries  to  the  seventh,  eighth,   and  ninth  intercostal  spaces 

(P-  7)- 

Triangularis  Sterni  (musculus  transversus  thoracis). — This 

is  a  thin  muscular  layer  placed  on  the  deep  surface  of  the 

sternum  and  costal  cartilages.      It  is  continuous  below  with  the 

transversalis  muscle  of  the  abdominal  wall,  and  arises  from 

the  posterior  surface  of  the  ensiform  cartilage,  the  lower  part 

of  the  body  of  the  sternum,  and  from  the  inner  ends  of  the 

5th,  6th,  and  7th  costal  cartilages.      From  this  origin  its  fibres 

radiate  in  an  upward  and  outward  direction,  and  separate  into 

five  slips,  which  are  inserted  into  the  deep  surfaces  and  lower 

borders  of  the  2nd,  3rd,  4th,  5th,  and  6th  costal  cartilages, 

close  to  their  junction  with  the  ribs  (Fig.  3). 

In  many  cases  the  muscle  is  feebly  developed,  and  does  not  show 
connections  so  wide  as  those  which  are  described  above.  Upon  the 
superficial  aspect  of  the  triangularis  sterni  are  placed  the  internal  mammary 
artery  and  the  series  of  intercostal  nerves. 

It  is  only  a  partial  view  of  the  muscle  which  is  obtained  in  the  present 
dissection,  but  it  is  not  advisable  to  remove  the  costal  cartilages  to  expose 
it  further,  as  this  would  materially  interfere  with  the  subsequent  display, 
in  their  proper  relations,  of  other  more  important  structures. 


THORACIC    CAVITY. 

The  arrangement  of  the  two  pleural  sacs  must  now  engage 
the  attention  of  the  student ;  but  in  order  that  the  relations 
of  these  may  be  understood,  it  is  necessary  that  the  dissector 
should  have  some  preliminary  knowledge  of  the  thoracic 
cavity  and  its  contents.  The  principal  viscera  of  the 
chest  are  the  lungs  and  the  heart.  The  two  lungs  occupy 
by  far  the  greatest  part  of  the  space,  and  lie  one  upon 
either  side  of  the  mesial  plane.  The  heart  is  placed 
between  the  lungs,  and  projects  more  into  the  left  than 
the  right  side  of  the  cavity.  It  is  completely  enveloped 
by  a  loose  conical  fibro- serous  sac  called  the  pericardium, 
which  is  attached  by  its  base  to  the  upper  surface  of  the 
diaphragm.  Each  lung  is  connected  with  the  base  of  the 
heart  by  several  large  vessels  which  pierce  the  pericardium, 
and  these,  with  the  corresponding  division  of  the  windpipe 
passing  to  the  lung,  constitute  the  pulmonary  root  or  pedicle. 
Each    lung    is    free    within    the    thorax   except    where  it    is 


THORACIC  CAVITY  u 

attached  by  its  root  and  by  a  fold  of  pleural  membrane 
which  will  afterwards  be  described  under  the  name  of  the 
liga??ientum  latum  pulmonis. 

The  thoracic  cavity  is  subdivided  into  two  large  lateral  chambers  which 
contain  the  lungs  by  a  central  vertical  partition  called  the  mediastinum 
thoracis.  This  partition  extends  from  the  anterior  thoracic  wall  in  front 
to  the  vertebral  column  behind,  and  from  the  fact  that  both  sides  of  it,  as 
well  as  the  other  walls  of  the  lateral  chambers,  are  lined  by  two  serous 
membranes  called  the  pleicrce,  the  chambers  receive  the  name  of  the  pletcral 
cavities. 

The  mediastinal  partition  is  built  up  of  the  several  structures  which  lie 
in  or  close  to  the  mesial  plane.  The  more  important  of  these  are  the  heart 
enveloped  in  its  pericardium,  the  thoracic  aorta  with  the  branches  which 
spring  from  its  arch,  the  pulmonary  vessels  and  great  veins  in  the 
neighbourhood  of  the  heart,  the  trachea,  the  gullet,  and  the  thoracic  duct 
and  the  vagus  and  phrenic  nerves. 

The  mediastinum  is  not  median  in  position.  Owing  to  the  marked  pro- 
jection of  the  heart  to  the  left  side  and  to  the  position  of  the  descending 
thoracic  aorta  on  the  left  side  of  the  bodies  of  the  vertebrce,  the  left  pleural 
chamber,  although  it  is  deeper  than  the  right,  is  considerably  reduced  in 
width.     The  two  pleural  cavities,  therefore,  are  not  symmetrical  in  form. 

Pleural  Sacs. — The  pleural  sacs  are  two  in  number,  one 
in  each  side  of  the  chest  cavity.  They  are  serous  sacs,  and 
therefore  closed.  Each  pleural  bag  is  so  disposed  that  it  not 
only  lines  the  chamber  in  which  the  lung  lies,  but  is  also 
reflected  over  the  lung  so  as  to  give  to  it  an  external  covering, 
which  is  intimately  connected  with  the  pulmonary  substance. 
We  recognise,  therefore,  in  connection  with  each  pleura  a 
lining  or  parietal  part,  and  an  investing  or  visceral  part.  It 
must  be  clearly  understood,  however,  that  these  terms  are 
merely  applied  to  indicate  different  portions  of  one  continuous 
membrane. " 

The  dissection  which  has  already  been  made  shows  the 
pleura  lining  the  deep  surface  of  the  costal  arches  and  internal 
intercostal  muscles.  This  portion  is  called  the  pleura  costalis. 
The  manner  in  which  the  pleura  of  each  side  is  reflected 
backwards  from  the  posterior  aspect  of  the  sternum  must 
now  be  investigated.  This  entails  a  somewhat  complicated 
dissection. 

Dissection. — The  sternum  must  be  divided  with  the  saw  into  four 
portions  by  three  separate  cuts,  viz.  (i)  a  transverse  section  through  the 
manubrium  sterni,  on  a  line  with  the  lower  margins  of  the  first  pair  of 
costal  cartilages;  (2)  a  transverse  cut  through  the  lower  part  of  the  body 
of  the  sternum,  in  the  interval  between  the  fifth  and  s/.\//i  costal  cartilages  ; 

an  oblique  section,  beginning  below  at  the  inferior  trai  at,  close 

to  the  left  margin  of  the  sternum,  and  carried  upwards  to  the  middle  of 


12 


THORAX 


the  superior  transverse  cut.  By  the  last  section  the  central  portion  of  the 
sternum  is  divided  into  two  lateral  pieces,  to  each  of  which  four  costal 
arches  are  attached  (Fig.  4). 

In  making  these  sections  through  the  sternum,  the  saw  should  only  be 
used  until  the  thick  periosteum  on  the  back  of  the  bone  is  reached.  This 
can  then  be  divided  cautiously  with  the  knife.  Of  course  the  internal 
mammary  vessels  must  be  preserved,  and  care  must  be  taken  not  to 
separate  the  parietal  pleura  at  any  point  from  the  deep  surface  of  the 
thoracic  wall. 

Anterior  Mediastinal  Space. — The  two  lateral  portions  of 
the    central    piece    of   the    sternum    should    now   be  gently 

separated  from  each  other, 
and,  on  looking  between 
them,  the  parietal  pleura 
of  each  side  will  be  seen 
leaving  the  posterior  sur- 
face of  the  sternum,  and 
passing  backwards  to  reach 
the  pericardium.  But  the 
pericardium  is  not  in  view, 
except  perhaps  to  a  small 
extent  below,  because  the 
two  pleural  membranes, 
where  they  make  this  re- 
flection, are  in  contact. 
Introduce  the  finger  be- 
tween the  two  pleural  sacs, 
and  pass  it  upwards  and 
downwards  through  the 
loose  areolar  tissue  which 

Fig.  4— Lines  along  which  the  Sternum     holds  them  together.      The 

should  be  divided.  pericardium  is  in  this  way 

exposed,  and  a  demonstra- 
tion is  obtained  of  a  space  which  is  termed  the  anterior 
mediastinal  space.  In  front  this  space  is  bounded  by  the 
posterior  surface  of  the  body  of  the  sternum,  and  usually 
also  by  the  inner  ends  of  the  fifth,  sixth,  and  seventh  costal 
cartilages  of  the  left  side,  clothed  by  the  left  triangularis 
sterni  muscle ;  behind,  by  the  pericardium ;  and  upon  each 
side,  by  the  pleura  as  it  passes  from  the  back  of  the 
sternum  to  the  front  of  the  pericardium.  In  its  upper 
part  the  space  can  hardly  be  said  to  exist,  seeing  that  the 
pleural  sacs  are  in  contact ;  but  below,  the  left  pleura  falls 
somewhat    short    of    the    right    pleura,    and    an    interval    is 


THORACIC  CAVITY  13 

apparent.  The  only  contents  to  be  noticed  in  the  anterior 
mediastinum  are,  in  its  lower  part,  a  few  small  lymphatic 
glands  and  some  loose  areolar  tissue,  in  which  ramify 
lymphatic  vessels  and  some  minute  arterial  twigs  from  the 
internal  mammary  artery. 

Dissection. — Having  now  ascertained  the  relations  of  the  pleura  to  the 
chest  wall,  proceed  to  the  study  of  its  other  connections  within  the  thorax. 
For  this  purpose  the  parietal  pleura  must  be  separated  from  the  ribs  as  far 
forwards  as  the  cartilages.  This  can  best  be  done  by  gently  insinuating 
the  forefinger  between  each  of  the  ribs  and  the  pleura,  and  then  running  it 
backwards  and  forwards.  Upon  no  account  detach  the  pleura  from  the 
cartilages.  Next  divide  with  the  knife  the  second,  third,  fourth,  fifth,  and 
sixth  costal  arches  at  the  junction  of  the  osseous  with  the  cartilaginous 
portions,  and  remove  these  ribs  by  snipping  through  them  with  the  bone 
pliers  as  far  back  as  possible.  The  sternum  and  cartilages,  to  which  the 
pleura  is  still  adherent,  must  be  left  in  position  until  the  arrangement  of 
the  membrane  has  been  thoroughly  investigated. 

The  greater  part  of  the  costal  pleura  now  lies  flaccid  upon  the  surface  of 
the  lung.  Make  a  vertical  incision  through  it,  midway  between  the  spine 
and  sternum,  from  the  level  of  the  second  costal  arch  down  as  far  as  the 
seventh  rib.  From  each  extremity  of  this  vertical  cut  carry  an  incision 
forwards  for  two  or  three  inches. 

Relations  of  the  Pleura. — A  considerable  piece  of  the 
parietal  pleura  can  now  be  thrown  forwards  like  a  door,  and 
the  interior  of  the  pleural  sac  is  exposed.  The  inner  surface 
of  the  membrane,  if  healthy,  presents  an  appearance  which  is 
characteristic  of  all  serous  membranes.  It  is  smooth,  polished, 
and  glistening,  and  is  moistened  by  a  small  amount  of  serous 
fluid.  It  is  thus  admirably  adapted  to  allow  the  movements 
of  the  lung  during  respiration  to  take  place  with  the  smallest 
possible  degree  of  friction.  When  the  surface  of  the  membrane 
becomes  roughened  by  inflammatory  exudation,  the  so-called 
"  friction  sounds  "  of  pleurisy  become  evident  when  the  ear  is 
applied  to  the  chest. 

Introduce  the  hand  into  the  pleural  sac,  and  explore  its 
extent  and  connections.  First  carry  it  inwards  behind  the 
costal  cartilages.  Its  passage  across  the  mesial  plane  of  the 
body  is  effectually  barred  by  the  reflection  of  the  pleural 
membrane  from  the  back  of  the  sternum  to  the  corresponding 
side  of  the  mediastinal  partition.  Above  the  level  of  the 
pericardium  it  passes  right  back  upon  the  upper  part  of  the 
mediastinal  partition  to  the  vertebral  column,  and  then 
proceeds  outwards  on  the  ribs.  Upon  that  part  of  the 
mediastinal  partition  which  is  formed  by  the  lateral  aspect 
of  the   pericardium  it  can  be   traced  backwards  towards  the 


M 


THORAX 


spine,  and  here  it  must  be  studied  from  two  points  of  view, 
viz.  (i)  at  the  level  of  the  root  of  the  lung,  and  (2)  below  the 
root  of  the  lung. 

At  the  level  of  the  pulmonary  root,  the  pleura  is  carried 
outwards,  so  as  not  only  to  envelop  this,  but  also  the  entire 
lung.  The  smooth  glistening  surface  of  the  organ  is  due  to 
the  pleural  investment  which  it  thus  acquires.  This,  then,  is 
the  visceral  pleura,  and  it  should  be  noticed  that  it  is  very 
much  finer  and  thinner  than  the  parietal  pleura.  Further,  it 
is  inseparably  attached  to  the  pulmonary  substance.      Behind 


Parietal  pleura 
Pleural  cavity  N 
Visceral  pleura 


sms6 


Parietal  pleura 
Pleural  cavity 
Visceral  pleura 


Fig.  5. — Diagrammatic  representation  of  a  cross  section  through 
the  two  Pleural  Sacs. 


the  root  of  the  lung  the  pleura  is  prolonged  backwards  upon 
the  pericardium,  and  on  the  left  side  over  the  descending 
thoracic  aorta  to  the  bodies  of  the  vertebrae.  On  the  right 
side  it  passes  from  the  pericardium  over  the  oesophagus  to  the 
bodies  of  the  vertebrae.  This  can  be  seen  by  tilting  forwards 
the  thick  posterior  border  of  the  lung.  From  the  vertebrae, 
the  pleura  passes  outwards  upon  the  deep  surfaces  of  the  ribs. 

Below  the  level  of  the  root  of  the  lung,  the  pleura  can  be 
traced  backwards  upon  the  pericardium  to  the  spine,  from 
which  it  is  conducted  outwards  upon  the  ribs.  But  it  does 
not  pass  backwards  uninterruptedly. 

The  same  two  layers  which  envelop  the  pulmonary  root 


THORACIC  CAVITY 


15 


are  prolonged  outwards  from  the  pericardium  in  apposition 


Thoracic  sym- 
pathetic cord 
Intercostal 
vessels  and  nerve 

Vena  azygos 
major 

Pulmonary   !u*V 
artery 

Eparterial  __J 
bronchus 

Hyparterial     I 

bronchus 


Pulmonar 
veins 


Scalenus  anticus 
Brachial  nerves 

Right  subclavian  artery 
Right  subclavian  vein 


Right  innominate  vein 
Internal  mammary  artery 
Trachea 
K  Right  vagus  nerve 

\ 
■^fc-  Left  innominate  vein 


(Esophagus 


Ligamentuni 
latum  pul- 
monis (cut) 


Ascending  aorta  and 
pulmonary  artery 

Superior 
vena  cava 


Internal  mam- 
mary artery 
Phrenic  nerve 
and  accom- 
Danying  artery 


Pericardium 
and  heart 


Diaphragm 


1  i<,.  6.  The  Right  Pleural  Chamber  opened  up  by  the  removal  <>f  its  outer 
wall.  The  lung  has  been  taken  away  so  as  to  expose  the  mediastinal 
wall  of  the  pleural  chamber.  Several  of  the  structures  in  the  medias- 
tinal septum  are  seen  shining  through  the  mediastinal  pleura 


1 6  THORAX 

with  each  other.  Meeting  the  inner  surface  of  the  lung, 
they  separate  to  enclose  the  lower  portion  of  this  organ. 
The  fold  of  pleura  which  is  thus  formed  is  called  the 
ligamentum  latum  pulmonis,  and  it  can  be  brought  into  view 
by  enlarging  the  opening  in  the  pleural  sac,  and  drawing  the 
basal  portion  of  the  lung  outwards  and  backwards.  It  will 
then  be  seen  to  be  a  fold  which  stretches  between  the 
pericardium  and  the  lower  part  of  the  inner  surface  of  the 
lung,  and  which  presents  a  free  border  below. 

The  dissector  has  now  traced  the  continuity  of  the  pleural 
sac  in  the  transverse  direction.  He  has  observed  that  it 
lines  the  deep  surface  of  the  costal  arches,  and  is  reflected 
backwards  upon  the  surface  of  the  intra-thoracic  mediastinal 
partition  from  the  back  of  the  sternum  to  the  spine.  This 
portion  is  called  the  mediastinal  pleura,  and  it  is  uninterrupted, 
except  where  it  is  pushed  outwards  over  the  lung  and  lung- 
root  in  the  form  of  an  investment.  But  the  continuity  of  the 
membrane  in  a  longitudinal  direction  must  also  be  established. 
This  inquiry  will  render  clear  its  relations  in  the  upper  and 
lower  parts  of  the  thoracic  cavity. 

In  the  upper  part  of  the  chest  cavity,  the  pleura  will  be 
observed  to  extend  upwards  through  the  thoracic  inlet  into 
the  root  of  the  neck,  and  to  form  in  this  locality  a  dome- 
shaped  roof  for  each  side  of  the  chest  (Fig.  n).  This 
portion  of  the  pleura  is  called  the  cervical  pleura.  Its  summit 
or  highest  point  reaches  the  level  of  the  lower  border  of  the 
neck  of  the  first  rib ;  but  owing  to  the  obliquity  of  the  first 
costal  arch  this  point  is  placed  from  one  to  two  inches  above 
the  anterior  extremity  of  the  first  rib,  and  from  a  half  to  one 
and  a  half  inches  above  the  clavicle.  The  subclavian  artery 
arches  over  and  lies  in  a  groove  on  the  inner  and  anterior 
aspect  of  this  cul-de-sac  near  its  summit,  whilst  at  a  lower  level 
the  innominate  and  subclavian  veins  also  lie  upon  its  inner 
and  anterior  aspects.  The  cervical  dome  of  pleura  is  supported 
on  its  outer  side  by  the  scalenus  anticus  and  scalenus  medius 
muscles,  and  is  strengthened  by  an  aponeurotic  expansion 
(Si&son's  fascia)  which  is  spread  over  it,  and  receives  attachment 
to  the  inner  concave  margin  of  the  first  rib.  This  fascia  is 
derived  from  a  small  muscular  slip  which  takes  origin  from  the 
transverse  process  of  the  seventh  cervical  vertebra.  It  may 
be  regarded  as  a  derivative  from  the  scalene  group  of  muscles. 

In   the   lower   part   of  the   thorax   the  parietal  pleura  is 


THORACIC  CAVITY  17 

reflected  from  the  inner  surface  of  the  chest  wall  on  to  the 


Scalenus  amicus 

Brachial  nerves 

Left  subclavian  artery 

Left  subclavian  vein 

Left  subclavian  artery 

Left  vagus  nerve 

Left  common  /    AA 

carotid  artery    / 
Left  innominate  vein   ^J^t 
Internal  mammary      && 
artery 
Phrenic  nerve  and 
accompanying 

artery  / 

Pulmonary      / 
artery   /■■   j 

Heart  and 


pericardium  tJC; 


Thoracic  duct 

<  Esophagus 

Recurrent  laryngeal 


Aortic  arch 


Left  pulmon- 
ary artery 

Left  bronchus 


Left  pulmon- 
ary veins 

Cut  edge  of 

parietal 

pleura 

Descending 

thoracic 

aorta 

Ligamentum 
a  turn 

pulmonis 

<  Esophagus 


Diaphragm 


Fig 


7. — The  Left  Pleural  Chamber  opened  up  by  the  removal  01  its  outer 
wall.  The  lung  has  been  taken  away  and  a  window  has  been  made 
into  the  superior  mediastinum  by  the  removal  of  a  portion  of  the  medias- 
tinal pleura.  Several  of  the  Structures  which  form  the  mediastinal 
partition  are  ieen  shining  through  the  mediastinal  pleura. 


VOL.   II — 2 


i8 


THORAX 


upper  surface  of  the  diaphragm,  and  is  carried  inwards  upon 
this  towards  the  base  of  the  pericardium,  where  it  becomes 
continuous  with  the  mediastinal  pleura.  The  portion  of 
the  membrane  which  clothes  the  diaphragm  is  termed  the 
diaphragmatic  pleura. 

Lines   of  Pleural    Reflection. — The  two  pleural   sacs   are 
not  shaped  alike.      The  chambers  which  they   line   are   not 

symmetrical,  and  con- 
sequently the  lines 
along  which  the  two 
membranes  are  re- 
flected from  the  ster- 
num and  costal  carti- 
lages backwards  to  - 
wards  the  pericardium, 
and  also  from  the  chest 
wall  on  to  the  dia- 
phragm, differ  some- 
what on  the  two  sides. 
First  consider  the 
sternal  line  of  reflection, 
or  that  along  which  the 
pleura  leaves  the  an- 
terior thoracic,  wall  to 
become  themediastinal 
pleura.  Behind  the 
manubrium  sterni  the 
two  pleural  sacs  are 
separated  from  each 
Fig.  8. — Diagram  to  show  the  relation  of  the  Other  by  an  angular 
lungs  and  the  pleural  sacs  to  the  anterior  interval  nnt  near  the 
thoracic  wall.      The  lungs  are  depicted  in  ,  f        , 

red,  and  the  pleural  sacs  in  blue.  upper       end       Ot        the 

gladiolus  they  come 
together,  and  proceed  downwards  in  close  contact,  and  slightly 
to  the  left  of  the  mesial  plane,  as  far  as  the  sternal  end  of 
the  fourth  costal  cartilage.  At  this  level  the  two  sacs  part 
company.  The  left  pleura  deviates  outwards,  whilst  the 
right  pleura  is  continued  downwards  in  a  straight  line  behind 
the  sternum  to  the  back  of  the  ensiform  cartilage.  Here  it 
turns  sharply  outwards,  and,  running  obliquely  downwards  and 
backwards  upon  the  deep  surface  of  the  seventh  costal  cartilage, 
is  reflected  from  this  on  to  the  upper  surface  of  the  diaphragm. 


THORACIC  CAVITY 


i9 


Opposite  the  sternal  end  of  the  fourth  costal  cartilage  the 
left  pleura  retires  in  an  outward  direction  from  the  right 
pleura,  and  descends  at  a  variable  distance  from  it,  so  as  to 
leave  a  small  triangular  portion  of  the  pericardium  uncovered 
by  pleura,  and  in  direct  contact  with  the  anterior  chest  wall. 

Cervical  dome  of  pleura 

Left  subclavian  artery 

Left  common  carotid  artery 

Left  innominate  vein 


Internal  mam- 
mary artery 

Anterior  margin 

of  right 

pleural  sac 


Intercostal  nerve      ^*     "V 


Pericardium  y     1 


Triangularis 
stern  i 


Diaphragm 


Fig.  9. — Diagram  to  show  the  parts  which  lie  in  front  of  the  pericardium 
and  heart.  The  outline  of  the  heart  is  indicated  in  red  by  a  dotted  line, 
and  the  anterior  margins  of  the  pleural  sacs  are  represented  by  blue  lines. 

This  area  is  very  variable  in  its  extent,  but  the  accompanying 
diagram  (Fig.  8)  may  be  considered  to  represent  the  average 
amount  of  outward  deviation  of  the  left  pleural  sac  in  con- 
nection with  this  part  of  the  chest  wall. 

Leaving  the  sternum,  the  reflection-line  of  the  left  pleura 
descends  parallel  and  close  to  the  left  margin  of  the  sternum 
behind  the  fourth  intercostal  space,  the  fifth  costal  cartilage, 
and  the  fifth  intercostal  space  to  the  back  of  the  sixth  costal 


20 


THORAX 


cartilage.     Here  it  turns  outwards  and  downwards  and  passes 
into  the  diaphragmatic  reflection-line. 

The  diaphragmatic  reflection-line  is   that   along   which    the 

CEsophagus 
Left  subclavian  artery 
Left  common  carotid  artery 
Left  superior  intercostal  vein 

Left  innominate  vein 

_Cut  edge  of 

parietal  pleura 


Aortic  arch 


Cut  edge  of 

parietal 

pleura 


Pericardium 


Pulmonary 
artery 

Bronchus 


Lower  pul- 
monary vein 


(Esophagus 


Diaphragmatic 
pleura 


Fig.  to. — Left  Pleural  Sac  in  a  subject  hardened  by  formalin  injection 
opened  into  by  the  removal  of  the  costal  pleura.  The  left  lung  has 
also  been  removed  so  as  to  display  the  mediastinal  pleura.  The  line 
along  which  the  pleura  is  reflected  from  the  diaphragm  on  to  the  thoracic 
wall  is  exhibited. 

pleura  leaves  the  thoracic  wall  and  is  reflected  on  to  the 
upper  surface  of  the  diaphragm.  This  reflection  takes  place 
along  a  curved  line  which,  except  behind  as  it  approaches  the 
vertebral  column,  is  placed  a  short  distance  above  the  lower 


THORACIC  CAVITY 


21 


border  of  the  thoracic  wall.  It  differs  slightly  on  the  two 
sides  of  the  body.  On  the  left  side  the  diaphragmatic  line 
of  reflection  proceeds  downwards  and  outwards  behind  the 


Cervical  dome  of  pleura 


Cut  edge  of 
parietal  pleura 

Trachea 

Vena  azygos 
major 


Bronchus 

(eparterial) 

Pulmonary 

artery 

Bronchus 

(hyparterial) 

Pulmonary  veins 


Inferior  vena 

cava 

Cut  edge  of 

parietal  pleura 


Right  innominate  vein 


Left  innominate 
vein 

Superior  vena 
cava 

Aorta  and  pul- 
monary artery 
within  the 
pericardium 

Cut  edge  of 
parietal  pleura 

Phrenic  nerve 
Pericardium 


Diaphragmatic 
pleura 


Pl6>  IT. — The  Right  Pleural  Sac  in  a  subject  hardened  by  formalin  injection 
opened  into  by  the  removal  of  the  costal  part  of  the  parietal  pleura.  The 
right  lung  has  also  been  removed  so  as  to  display  the  right  mediastinal 
pleura.      Note  the  line  of  diaphragmatic  reflection  of  the  pleura. 

ascending  part  of  the  sixth  costal  cartilage,  crosses  behind  the 
anterior  end  of  the  sixth  intercostal  space  and  the  descending 
part  of  the  seventh  costal  cartilage.  Still  continuing  to 
descend,  it  passes  behind  the  eighth  costal  arch  at  the  junction 
n— 2  a 


22 


THORAX 


between  its  cartilaginous  and  bony  parts.  This  is  a  fairly 
constant  relation  on  both  sides  of  the  body,  and  it  should  be 
noted  that  a  vertical  line  drawn  downwards  from  the  nipple 
(mammillary  line)  intersects  the  line  of  pleural  reflection  close 
to  the  point  where  it  presents  this  relation  to  the  eighth  costal 
arch.      Beyond  this  point  the  line  of  diaphragmatic  reflection 


Crus  of  diaphragm 


Crus  of  diaphragm 


Ligamentum 
arcuatum  externum 


Diaphragm 


Spleen 


Intestine 


Ligamentum 

arcuatum 

externum 


Diaphragm 


Liver 


Ascending 
colon 


Fig.  12. — Dissection  of  a  subject  hardened  by  formalin  injection  to  show 
the  relations  of  the  Pleural  Sacs  posteriorly  ;  more  especially  to  the 
kidneys  and  last  ribs. 


is  carried  downwards  and  outwards  across  the  extremities  of 
the  bony  portions  of  the  ninth  and  tenth  ribs.  As  it  passes 
under  cover  of  the  tenth  rib,  or  it  may  be  as  it  proceeds  across 
the  tenth  intercostal  space,  the  line  of  pleural  reflection  reaches 
its  lowest  point,  and  it  is  important  to  observe  that  this  point 
lies  in  the  mid-lateral  line  (i.e.,  a  vertical  line  drawn  downwards 
on  the  side  of  the  chest  midway  between  spine  and  sternum). 
From  this  it  curves  slightly  upwards  as  it  proceeds  backwards 
to  the  spine.     Thus  it  cuts  across  the  eleventh  rib  and  reaches 


THORACIC  CAVITY  23 

the  twelfth  rib.  The  relation  which  it  presents  to  the  twelfth 
rib  varies  in  accordance  with  the  length  of  that  bone.  When 
the  rib  is  not  unusually  short,  the  pleura  clothes  its  inner  half 
and  the  line  of  reflection  falls  below  this  portion  of  the  rib  so 
as  to  meet  the  spine  midway  between  the  head  of  the  last  rib 
and  the  transverse  process  of  the  first  lumbar  vertebra.  Here 
therefore  the  line  of  diaphragmatic  reflection  falls  below  the 
lower  border  of  the  thoracic  wall,  and  this  is  a  point  of  high 
practical  importance.  In  operations  on  the  kidney  the  incision 
cannot  be  carried  above  the  level  of  the  transverse  process 
of  the  first  lumbar  vertebra  and  the  ligamentum  arcuatum 
externum  without  the  risk  of  wounding  the  pleura  (Fig.  12). 

On  the  right  side  the  line  of  diaphragmatic  pleural  reflection 
differs  from  that  on  the  left  side  chiefly  in  front.  Here  it 
descends  to  a  lower  level.  Thus  it  proceeds  outwards  behind 
the  ascending  part  of  the  seventh  costal  cartilage,  but  it  cuts 
the  eighth  costal  arch,  as  a  rule,  at  the  same  point  as  on  the 
left  side,  viz.,  at  the  junction  between  its  cartilaginous  and  bony 
portions.  From  this  backwards  to  the  spine  the  relations  are 
so  similar  to  those  of  the  left  side  that  a  separate  description 
is  unnecessary. 

It  is  commonly  stated  that  the  left  pleural  sac  reaches  a  lower  level  than 
the  right.  This  is  by  no  means  the  rule.  In  those  cases  where  the  two 
pleural  sacs  do  not  reach  the  same  level  at  their  lowest  points  it  is  some- 
times the  right  and  sometimes  the  left  pleura  which  oversteps  the  mark. 

In  the  dissection  of  the  intercostal  spaces  a  strong  fascia 
has  been  observed  to  pass  from  the  uncovered  part  of  the 
diaphragm  and  from  the  costal  cartilages  to  the  surface  of  the 
costal  pleura  along  the  line  of  diaphragmatic  reflection.  It  may 
be  compared  with  Sidsori's  fascia,  which  covers  the  cervical 
pleura,  but  is  more  strongly  marked  and  more  tendinous 
in  character.      It  may  be  termed  the  phrenico-pleural  fascia. 

Mediastinal  Space. — The  term  mediastinal  space  is  applied 
to  the  interval  which  is  left  between  the  two  pleural  sacs.  It 
is  within  this  space  that  by  far  the  greater  part  of  the  dissec- 
tion of  the  thorax  has  to  be  conducted,  and,  consequently, 
it  is  important  that  the  student  should  acquire  an  accurate 
conception  of  its  extent  and  connexions.  We  have  noted 
that  the  mediastinal  portion  of  the  pleura  extends  backwards 
from  the  front  wall  of  the  thorax  on  either  side  of  the  mesial 
plane,  on  the  surface  of  the  intra-thoracic  mediastinal  partition. 
This  forms  the  lateral  boundary  of  the  space,  whilst  in  front 

II— 2  b 


24  THORAX 

it  is  bounded  by  the  sternum,  and  behind  by  the  vertebral 
column.  But  it  is  customary  to  subdivide  in  an  arbitrary 
manner  the  mediastinal  space  into  four  portions,  termed 
respectively  superior,  anterior,  middle,  and  posterior,  according 
to  the  relations  which  they  present  to  the  pericardium. 

Superior  Mediastinum. — This  is  the  part  of  the  general 
mediastinal  space  which  lies  above  the  level  of  the  pericardium. 
Its  boundaries  are  the  following  : — In  front,  the  manubrium 
sterni,  to  the  posterior  aspect  of  which  are  attached  the  lower 
ends  of  the  sterno-hyoid  and  sterno-thyroid  muscles ;  behind, 
the  upper  four  dorsal  vertebrae  with  the  longus  colli  muscles  ; 
below,  an  imaginary  and  oblique  plane  extending  from  the 
lower  border  of  the  manubrium  sterni  backwards  and  upwards 
to  the  lower  border  of  the  fourth  dorsal  vertebra  ;  and  laterally, 
the  mediastinal  pleura  as  it  extends  on  each  side  from  the 
back  of  the  sternum  to  the  vertebral  column. 

Figs.  38  and  40  (pp.  68  and  71)  are  reproduced  from 
tracings  of  two  sections  through  the  superior  mediastinum 
at  different  levels.  Fig.  40  represents  a  section  through  its 
upper  part,  and  Fig.  38  a  section  through  its  lower  part  at 
the  level  of  the  fourth  dorsal  vertebra.  The  boundaries,  form, 
and  contents  of  the  space  are  clearly  seen'. 

Within  the  superior  mediastinum  are  placed — (1)  the  aortic 
arch,  and  the  three  great  vessels  which  spring  from  it ;  (2)  the 
innominate  veins  and  the  upper  part  of  the  superior  vena  cava; 
(3)  the  trachea,  gullet,  and  thoracic  duct;  (4)  the  vagus, 
phrenic,  left  recurrent  laryngeal,  and  cardiac  nerves ;  (5)  the 
thymus  gland.  The  relative  positions  of  these  structures  can 
be  studied,  in  the  meantime,  in  Figs.  38  and  40  ;  afterwards 
they  will  be  displayed  in  the  course  of  dissection. 

Middle  Mediastinum. — This  is  the  wide  middle  part  of  the 
space  which  contains  the  pericardium,  and  lies  below  the 
superior  mediastinum.  In  addition  to  the  pericardium  and 
its  contents,  the  middle  mediastinum  contains  the  phrenic 
nerves  and  their  arteriae  comites. 

Anterior  Mediastinum. — The  anterior  mediastinum  is  that 
portion  of  the  inter-pleural  space  which  lies  between  the 
pericardium  behind  and  the  body  of  the  sternum  in  front. 
It  has  already  been  examined  (p.  12). 

Posterior  Mediastinum. — This  is  situated  between  the 
pericardium  and  the  bodies  of  the  vertebrae.  It  will  be 
studied  later  on. 


THORACIC  CAVITY 


25 


Dissection. — The  central  portion  of  the  sternum,  with  the  attached  costal 
cartilages,  may  now  be  removed  and  laid  aside  until  a  suitable  opportunity 
arises  for  the  study  of  the  chondro-  sternal  joints.  Carefully  strip  the 
mediastinal  pleura  from  the  side  of  the  pericardium.  This  will  bring  into 
view  the  phrenic  nerve  and  the  slender  arteria  comes  nervi  phrenici,  a 
branch  of  the  internal  mammary  artery  which  accompar 'es_  the  phrenic 
nerve  upon  the  side  of  the  pericardial  sac.  During  this  dissection  the 
minute  mediastinal  and  thymic  branches  of  the  internal  mammary  artery 
will  be  brought  into  view. 

Lungs  (pulmones). — The  lungs  are  two  soft,  spongy  organs 
placed  one  on  either  side  of  the  mediastinal  space.     When 


Subclavian  sulcus 
Groove  for 
innominate  vein  ^^ 


Subclavian  sulcus 

Groove  for 
innominate  vein 


Lower  lobe  Cardiac  notch 

Fig.   13. — The  Trachea,  Bronchi,  and  Lungs  of  a  Child,  hardened 
by  formalin  injection. 

the  thorax  is  opened  (unless  they  have  been  hardened  in  situ) 

they  collapse  to  about  one-third  of  their  original  bulk,  and  it 

is  difficult  for  the  student  to  realise  their  proper  dimensions 

and  shape. 

In  the  event  of  the  lungs  not  having  been  hardened  in  situ  by  formalin 
injection,  the  dissector  of  the  thorax  may  {with  the  consent  of  the  dissector 
of  the  head  and  neck)  introduce  the  nozzle  of  the  bellows  into  the  cervical 
part  of  the  trachea  so  as  to  inflate  the  lungs  with  air.  A  truer  conception 
of  these  organs  will  thus  be  obtained,  and  a  demonstration  will  be  afforded 
of  their  high  elasticity,  and  of  their  connection  with  the  windpipe. 

When    healthy  and  sound,   the   lungs   lie   free  within  the 


26 


THORAX 


cavity  of  the  chest,  and  are  only  attached  by  their  roots  and 
by  their  ligamenta  lata.  It  is  rare,  however,  that  a  healthy 
lung  is  seen  in  the  dissecting-room.  Adhesions  between  the 
visceral  and  parietal  portions  of  the  pleura  due  to  pleurisy 
are  generally  present.  Each  lung  is  accurately  adapted  to 
the  space  in  which  it  lies,  and,  in  the  natural  state,  it  bears 
on  its  surface  impressions  and  elevations  which  are  an  exact 
counterpart  of  the  inequalities  of  the  parts  with  which  its 
surfaces  are  in  contact. 

In  its  natural  condition,  before  the  chest  is  opened,  each 
lung  is  conical  in  form,  and  presents  for  examination  an  apex, 
a  base,  an  outer  and  an  inner  surface,  and  an  anterior  and  a 


Vagus  nerve 


Trachea 


(Esophagus 


Right 
subclavian  artery 
Right  s 
innominate  vein 


Innominate 
artery 


Left  subclavian  artery 

Sulcus  subclavius 


Vagus  nerve 


Left 
_  common 
carotid 
Left 

.innominate 

vein 


Fig.  14. — Cervical  Domes  of  the  Pleural  Sacs,  and  parts  in  relation  to  them. 


posterior  border.  The  apex  of  the  lung  (apex  pulmonis)  is 
blunt  and  rounded,  and  rises  above  the  level  of  the  oblique 
first  costal  arch  to  the  full  height  of  the  cervical  dome  of  the 
pleura.  It  therefore  protrudes  upwards  into  the  root  of  the 
neck.  The  subclavian  artery  arches  outwards  on  its  inner 
and  anterior  aspects  a  short  distance  below  its  summit,  and 
a  groove  (sulcus  subclavius)  corresponding  to  the  vessel  is 
apparent  upon  it.  At  a  lower  level  on  the  apex  pulmonis 
a  shallower  and  wider  groove  upon  its  inner  and  anterior 
aspects  marks  the  position  of  the  innominate  and  subclavian 
veins.  Although  these  vessels  impress  the  lung,  they  are 
separated  from  it  by  the  cervical  pleura.  The  base  of  the  lung 
(basis  pulmonis)  presents  a  semilunar  outline,  and  is  adapted 
to  the  upper  surface  of  the  diaphragm.  Consequently,  it  is 
deeply  hollowed  out ;  and  as  the  right  cupola  of  the  diaphragm 


THORACIC   CAVITY 


27 


ascends  higher  than  the  left,  the  basal  concavity  of  the  right 
lung  is  deeper  than  that  of  the  left  lung.  Laterally,  and 
behind,  the  base  of  each  lung  is  limited  by  a  thin  sharp 
margin,  which  passes  downwards  in  the  narrow  pleural  recess 
(sinus  phrenico-costalis)  between  the  diaphragm  and  chest  wall. 
This  margin  extends  much  lower  down  behind  and  at  the 
outer  side  than  in  front,  but  it  falls  considerably  short  of  the 
bottom  of  the  phrenico-costal  sinus  of  pleura. 


Groove  for  innominate  artery 


Groove  for  vena  azygos  major 

Groove  for  superior 
vena  cava 


Bronchial  gland 


Pulmonary  artery 


Bronchus 


Cardiac  surface 


Pulmonary 


Surface  for 
oesophagus 


Ligamentum  latum.pulmonis 
FIG.   15.— The  Mediastinal  Surface  of  a  Right  Lung  hardened  in  situ. 

The  bases  of  the  lungs  establish  important  relations  with  the  viscera, 
which  occupy  the  costal  zone  of  the  abdominal  cavity  — the  diaphragm 
alone  intervening.  Thus  the  base  of  the  right  lung  rests  upon  the  right 
lobe  of  the  liver  ;  whilst  the  base  of  the  left  lung  is  in  relation  to  the  left 
lobe  of  the  liver,  the  stomach,  the  spleen,  and  in  some  cases  to  the  splenic 
flexure  of  the  colon. 

The  outer  surface  of  the  lung  (facies  costalis  pulmonis)  is 
very  extensive  and  is  full  and  convex.  It  is  in  relation  to  the 
parietal  pleura,  as  it  clothes  the  ribs  and  intercostal  muscles, 
and  it  bears  the   impress  of  the  costal  arches.     The  inner  or 


28 


THORAX 


mediastinal  surface  (facies  mediastinalis  pulmonis)  presents  a 
smaller  area  than  the  outer  surface.  It  is  applied  to  the 
mediastinal  partition,  and  presents  markings  which  are  the 
exact  counterpart  of  the  inequalities  upon  this  septum.  Thus 
it  is  deeply  hollowed  out  in  adaptation  to  the  pericardium 
upon  which  it  fits.  This  pericardial  concavity  comprises  the 
greater   part   of  the    mediastinal  surface,   and,   owing  to  the 


Sulcus  subclavius 


Groove  for  aortic  arch 
Fissure  in  lung 


Bronchial  gland 


Groove  for 
descending  aorta 


Groove  for  innominate  vein 

>.      /Pulmonary  artery 
\  ^'Bronchus 
%\^- Pulmonary  veins 


Cardiac 
depression 


Surface  in  apposition 
with  oesophagus 

Ligamentum  latum  pulmonis 
Fig.  16. — Inner  or  Mediastinal  Aspect  of  a  Left  Lung  hardened  in  situ. 

greater  projection  of  the  heart  to  the  left  side,  it  is  much 
deeper  and  more  extensive  in  the  left  lung  than  in  the  right 
lung.  Above  and  behind  the  pericardial  hollow  is  the  hilum 
of  the  lung.  This  is  a  wedge-shaped  depressed  area,  within 
which  the  vessels,  nerves,  lymphatics,  together  with  the 
bronchus,  enter  and  leave  the  organ.  The  hilum  is  surrounded 
by  the  reflection  of  the  pleura  from  the  surface  of  the  lung 
on  to  the  pulmonary  root.  Behind  the  hilum  and  the  peri- 
cardial area  there  is  a  narrow  strip  of  the  inner  surface  of  the 
lung  which  is  in  relation  to  the  lateral  wall  of  the  posterior 
mediastinum.      On  the  right  lu?ig  this  part  of  the  surface  is 


THORACIC  CAVITY  29 

depressed  and  corresponds  to  the  oesophagus  ;  on  the  left  lung 
it  presents  a  broad  longitudinal  groove  which  is  produced  by 
the  contact  of  the  lung  with  the  descending  thoracic  aorta, 
and  also,  close  to  the  base,  a  small  triangular  flattened  area 
in  front  of  this  which  is  applied  to  the  oesophagus  where  it 
pierces  the  diaphragm. 

The  portion  of  the  inner  surface  of  the  lung  which  lies 
above  the  hilum  and  pericardial  hollow  is  applied  to  the  lateral 
aspect  of  the  superior  mediastinum,  and  the  markings  are 
accordingly  different  on  the  two  sides.  On  the  left  lung  a 
broad  deep  groove  produced  by  the  aortic  arch  curves  over 
the  hilum  and  becomes  continuous  with  the  aortic  groove  on 
the  posterior  mediastinal  surface.  From  this  a  narrower, 
deeper,  and  much  more  sharply  cut  groove  ascends  and  turns 
outwards  over  the  apex  pulmonis  a  short  distance  from  the 
summit.  This  is  the  sulcus  subclavius,  and  it  contains  the 
left  subclavian  artery  when  the  lung  is  in  its  place.  In  front 
of  this  a  shallow  wide  groove,  also  leading  up  to  the  front  of 
the  apex,  corresponds  to  the  left  innominate  vein.  In  the 
right  lung  the  hilum  is  circumscribed  above  by  a  narrow  curved 
groove  which  lodges  the  vena  azygos  major  as  it  turns 
forward  to  join  the  superior  vena  cava.  From  the  anterior 
end  of  the  azygos  sulcus  a  wide  shallow  groove  leads  upwards 
to  the  lower  part  of  the  apex  pulmonis.  This  is  produced  by 
the  vena  cava  superior  and  the  right  innominate  vein.  Close 
to  the  summit  of  the  apex  there  is  also,  on  its  inner  aspect, 
a  sulcus  for  the  upper  part  of  the  innominate  artery. 

The  two  borders  of  the  lung  offer  a  marked  contrast  to 
each  other.  The  anterior  border  is  short,  thin,  and  sharp,  and 
extends  forwards  and  inwards  in  front  of  the  pericardium  into 
the  narrow  pleural  recess  behind  the  sternum  and  costal 
cartilages  {sinus  costo-mediastinalis).  It  begins  abruptly  above, 
immediately  below  the  groove  on  the  apex  for  the  innominate 
vein,  and  extends  down  to  the  base,  where  it  becomes  con- 
tinuous with  the  sharp  basal  border.  The  posterior  border  of 
the  lung  is  thick,  long,  and  rounded.  It  forms  the  most  bulky 
part  of  the  organ,  and  occupies  the  deep  hollow  of  the  thoracic 
cavity  which  is  placed  on  each  side  of  the  spine. 

Differences  between  the  two  Lungs. — There  are  some 
points,  besides  those  already  mentioned,  in  which  the  two 
lungs  differ  from  each  other: — (1)  The  right  lung  is  slightly 
larger  than  the  left,  in  the  proportion  of  1 1  to  10.      (2)  The 


3o  THORAX 

right  lung  is  shorter  and  wider  than  the  left  lung.  This 
difference  is  due  to  the  great  bulk  of  the  right  lobe  of  the 
liver,  which  elevates  the  right  cupola  of  the  diaphragm  to  a 
higher  level  than  the  left  cupola,  and  likewise  to  the  heart 
and  pericardium,  projecting  more  to  the  left  than  the  right, 
and  thus  diminishing  the  width  of  the  left  lung.  (3)  The 
anterior  sharp  margin  of  the  right  lung  is  more  or  less 
straight ;  the  corresponding  margin  of  the  left  lung  presents, 
in  its  lower  part,  a  marked  angular  deficiency  (incisura  cardiacd) 
for  the  reception  of  the  apex  of  the  heart  and  the  pericardium. 
(4)  The  right  lung  is  subdivided  into  three  lobes,  and  the 
left  lung  into  two. 

Lobes  of  the  Lungs. — The  left  lung  is  divided  into  two 
lobes  by  a  long  oblique  deep  fissure  which  penetrates  its 
substance  to  within  a  short  distance  of  the  hilum.  This  fissure 
begins  above  at  the  posterior  border,  about  two  and  a  half 
inches  below  the  apex,  and  about  the  level  of  the  vertebral 
end  of  the  third  rib,  and  is  continued  on  the  outer  surface  in 
a  somewhat  spiral  direction  downwards  and  forwards  to  the 
anterior  end  of  the  base  of  the  lung.  The  upper  lobe  of  the 
lung  (lobus  superior)  lies  above  and  in  front  of  this  cleft.  It 
is  conical  in  form  with  an  oblique  base.  The  apex  and  the 
whole  of  the  anterior  border  belong  to  it.  The  lower  lobe 
(lobus  inferior),  somewhat  quadrangular,  lies  below  and  behind 
the  fissure,  and  belonging  to  it  we  recognise  the  entire  base 
and  the  greater  part  of  the  thick  posterior  border.  It  is 
therefore  the  more  bulky  of  the  two. 

In  the  right  lung  there  are  two  fissures  subdividing  it  into 
three  lobes.  One  of  these  fissures  is  very  similar  in  its  posi- 
tion and  relations  to  the  fissure  in  the  left  lung.  It  is, 
however,  more  vertical  in  its  direction,  and  ends  below  some- 
what farther  outwards.  It  separates  the  lower  lobe  from  the 
upper  and  middle  lobes.  The  second  cleft  begins  in  the 
main  fissure  at  the  posterior  border  of  the  lung,  and  proceeds 
horizontally  forwards  on  the  outer  surface  to  end  at  the 
anterior  border  of  the  lung  at  the  level  of  the  fourth  costal 
cartilage.  The  middle  or  intermediate  lobe  is  wedge-shaped 
in  outline. 

Root  of  the  Lung  (radix  pulmonis). — This  is  the  term 
which  is  applied  to  a  number  of  structures  which  enter  the 
lung  at  the  hilum  or  slit  upon  its  inner  mediastinal  surface. 
These  structures  are  held  together  by  an  investment  of  pleura, 


THORACIC  CAVITY  31 

and  constitute  a  pedicle  which  attaches  the  lung  to  the 
mediastinal  wall  of  the  pleural  cavity. 

The  pleura  should  be  carefully  stripped  from  around  the 
root  of  the  lung;  but,  before  undertaking  the  dissection  of 
the  structures  which  compose  the  root,  the  relation  which  it 
bears  to  neighbouring  parts  should  be  determined. 

In  front  there  are — (1)  a  delicate  plexus  of  nerves,  the 
anterior  pulmonary  plexus;  and  (2)  the  phrenic  nerve  with 
the  arteria  comes  nervi  phrenici.  Behind,  the  pneumogastric 
nerve  breaks  up  into  the  posterior  pulmonary  plexus ;  whilst 
inferiorly,  there  is  the  ligamentum  latum  pulmonis.  These 
are  the  relations  which  are  common  to  the  root  of  the  lung 
upon  both  sides  of  the  body,  but  there  are  others  which  are 
peculiar  to  each  side. 

On  the  right  side — (1)  The  vena  azygos  major,  as  it  curves 
forwards  over  the  right  bronchus  to  join  the  superior  vena 
cava,  is  in  relation  to  the  upper  border  of  the  pulmonary 
root;  (2)  the  superior  vena  cava,  in  the  lower  part  of  its 
course,  lies  in  front  of  the  pulmonary  root. 

On  the  left  side,  the  aorta  arches  over  the  root  of  the  lung, 
and  the  descending  thoracic  aorta  passes  down  behind  it. 

Dissection.— Now   proceed  to  dissect   out   the  constituent   parts  of  the 
root  of  the  lung. 

Constituent  parts  of  the  Pulmonary  Root. — The  most 
important  structures  which  enter  into  the  formation  of  the 
pulmonary  root  are — (1)  the  two  pulmonary  veins;  (2)  the 
pulmonary  artery;  (3)  the  bronchus.  But,  in  addition  to 
these,  there  are  one  or  more  small  bronchial  arteries  and 
veins,  the  pulmonary  nerves,  the  puh?wnary  ly??iphatic  vessels, 
and  some  bronchial  glands.  These  are  bound  together  by 
some  loose  areolar  tissue,  and  the  whole  pedicle  so  constituted 
is  invested  by  pleura. 

The  pulmonary  nerves  are  derived  from  the  anterior  and 
posterior  pulmonary  plexuses.  The  anterior  pulmonary  plexus 
is  composed  of  two  or  three  delicate  filaments,  which  come 
from  the  pneumogastric  nerve  before  it  reaches  the  posterior 
aspect  of  the  pulmonary  root.  These  join  with  the 
sympathetic  twigs  on  the  wall  of  the  pulmonary  artery. 
The  deep  cardiac  plexus  gives  twigs  to  the  anterior  pul- 
monary plexus  on  both  sides  of  the  body,  and  the  plexus  of 
the  left  side  likewise  receives  a   few  filaments  from  the  super- 


32  THORAX 

ficial  cardiac  plexus.  It  is  only  under  the  most  favourable 
circumstances  that  a  good  view  of  these  nerves  can  be 
obtained. 

Dissection. — The  posterior  pulmonary  plexus  is  easily  dissected.  To 
get  at  it,  the  lung  must  be  thrown  well  forwards  over  the  pericardium, 
and  the  pleura  stripped  from  the  posterior  surface  of  the  pulmonary 
root.  The  pneumogastric  nerve  should  then  be  secured  and  followed 
downwards.  On  the  left  side  it  will  be  found  crossing  the  aortic  arch  ; 
on  the  right  side  it  lies  by  the  side  of  the  trachea. 

The  posterior  pulmonary  plexus  is  formed  by  the  entire 
trunk  of  the  pneumogastric  nerve  breaking  up  into  a 
flattened  network  immediately  under  cover  of  the  pleura 
upon  the  posterior  aspect  of  the  root  of  the  lung.  Several 
minute  twigs  from  the  upper  thoracic  ganglia  of  the  sym- 
pathetic enter  this  plexus.  The  posterior  pulmonary  plexuses 
of  opposite  sides  are  connected  by  some  strong  branches, 
which  cross  the  mesial  plane  in  front  of  and  behind  the 
oesophagus.  From  both  the  anterior  and  posterior  pulmonary 
plexuses  fine  twigs  are  prolonged  into  the  lung  along  the 
divisions  of  the  bronchi.  The  posterior  branches,  however, 
are  much  larger  than  the  anterior. 

The  bronchial  arteries  (arterise  bronchiales),  one  to  three  in 
number  on  each  side,  are  the  proper  nutrient  vessels  of  the 
lung.  They  are  placed  on  the  posterior  aspect  of  the  root 
of  the  lung,  and  have,  no  doubt,  been  exposed  in  the  dis- 
section of  the  posterior  pulmonary  plexus.  As  a  general 
rule  they  lie  in  close  contact  with  the  back  of  the  corre- 
sponding bronchus  and  follow  it  into  the  lung. 

Part  of  the  blood  conveyed  to  the  lungs  by  the  bronchial 
arteries  is  returned  by  the  pulmonary  veins ;  the  remainder 
is  returned  by  special  bronchial  veins,  which  open  on  the 
right  side  into  the  vena  azygos  major,  and  on  the  left  side 
into  the  vena  azygos  minor  superior. 

Dissection. — The  pulmonary  vessels  and  the  bronchus  should  now  be 
separated  from  each  other  with  the  handle  of  the  knife,  and  their  relative 
positions  in  the  root  of  the  lung  studied.  This  dissection  should  be  made, 
not  only  in  front,  but  also  behind,  so  that  the  parts  may  be  thoroughly 
isolated  and  rendered  distinct.  Hardened  and  blackened  bronchial 
glands  sometimes  make  the  dissection  a  difficult  one.  These  must  be 
removed. 

The  bronchus  lies  in  the  posterior  part  of  the  root  of  the 
lung  behind  both  the  pulmonary  artery  and  the  higher  of 
the  two    pulmonary  veins.     The  pulmonary  artery   holds   an 


THORACIC  CAVITY 


33 


intermediate  position,  whilst  the  higher  of  the  two  pulmonary 
veins  is  placed  in  front  of  the  artery.  When  examined  in 
respect  to  their  relations  from  above  downwards,  the  right 
and  left  pulmonary  roots  are  seen  to  differ  from  each  other. 
On  both  sides  the  veins  occupy  the  lowest  level — the  lower 
vein  being  situated  in  the  very  lowest  part  of  the  hilum  of  the 
lung.  On  the  right  side  the  bronchus  is  highest  and  the 
artery  intermediate,  whereas  on  the  left  side  the  artery  is 
highest  and  the  bronchus  intermediate  in  position.  The 
different  position  of  the  bronchus  in   the  roots  of  the  lungs 


EPARTERIAL 
BRONCHUS 


Reflection 
pleura 


Pulmonary 
veins 


Fig.  17. 


Ligamentum  latum  pulmonis 


-The  two  Pulmonary  Roots  transversely  divided  close  to  the 
hilum  of  each  kins:. 


is  due  to  the  fact  that  on  the  right  side  a  branch  which  is  topo- 
graphically not  represented  on  the  left  side  arises  from  the 
bronchus  a  short  distance  from  its  origin,  and  proceeds  almost 
horizontally  outwards  to  the  upper  lobe  of  the  lung.  This 
division  lies  above  the  level  of  the  pulmonary  artery,  and  in 
consequence  receives  the  name  of  the  eparterlal  bronchus.  The 
other  branches  of  the  right  bronchus,  and  all  the  branches 
of  the  left  bronchus,  lie  below  the  level  of  the  main  trunk 
of  the  corresponding  pulmonary  artery,  and  are  termed  hyp- 
arterial  bronchi. 

Phrenic  Nerve  (nervus  phrenicus). — This  is  a  long  nerve 
which  arises  in  the  neck  from  the  cervical  plexus,  and 
traverses     the    entire    length    of    the    mediastinal     space    to 

vol.  11 — 3 


34  THORAX 

reach  the  diaphragm.  It  has  already  been  exposed  upon 
the  lateral  aspect  of  the  pericardium  in  front  of  the  root 
of  the  lung.      Follow  it  upwards  and  downwards. 

The  phrenic  nerve  enters  the  chest  cavity  through  the 
thoracic  inlet,  and  as  it  does  so  it  passes  behind  the  sub- 
clavian vein,  and  crosses  obliquely  the  internal  mammary 
artery  in  a  direction  from  without  inwards.  It  now  proceeds 
downwards  through  the  superior  mediastinum  into  the 
middle  mediastinum.  In  the  latter  it  is  applied  to  the 
side  of  the  pericardium  in  front  of  the  root  of  the  lung, 
and  is  covered  by  the  mediastinal  pleura.  Finally  reaching 
the  diaphragm,  the  nerve  breaks  up  into  several  branches 
which  pierce  its  substance  and  spread  out  on  its  under 
surface. 

But  the  two  phrenic  nerves  of  opposite  sides  present 
certain  differences.  They  differ  (i)  in  length;  and  (2)  in 
certain  of  their  relations. 

The  left  phrenic  is  the  longer  of  the  two  nerves,  and  this 
is  due  partly  to  the  greater  projection  of  the  heart  and 
pericardium  to  the  left  side,  and  partly  to  the  fact  that  the 
left  cupola  of  the  diaphragm  which  it  enters  does  not  rise 
so  high  as  the  right  cupola.  The  differences  in  relationship 
are  the  following  : — (1)  As  they  traverse  the  superior  media- 
stinum the  left  phrenic  nerve  crosses  the  vagus  nerve  and  the 
aortic  arch,  whilst  the  right  phrenic  nerve  lies  in  relation  to 
the  right  side  of  the  right  innominate  vein  and  the  superior 
vena  cava;  (2)  one  or  more  of  the  terminal  branches  of  the 
right  nerve  pass  through  the  opening  in  the  diaphragm  for 
the  inferior  vena  cava. 

The  branches  of  the  phrenic  are  chiefly  destined  for  the 
supply  of  the  diaphragm,  but  in  its  course  through  the  middle 
mediastinum  it  gives  a  few  fine  filaments  to  the  pericardium 
and  the  pleura. 

The  small  branch  of  the  internal  mammary  artery  which 
accompanies  the  phrenic  nerve,  the  arteria  comes  nervi  phrenici, 
may  be  traced  in  a  well-injected  subject  to  the  fore-part  of 
the  diaphragm.  It  takes  origin  high  up  in  the  thorax,  and 
gives  branches  to  the  pericardium. 

Superficial  Cardiac  Plexus. — The  best  plan  to  adopt  in 
making  a  dissection  of  these  delicate  nerve  filaments  is. to 
begin  by  securing  the  two  cardiac  nerves  which  enter  the 
plexus  from  above.     These  are — (1)  the  cardiac  branch  from 


THORACIC  CAVITY  35 

the  superior  cervical  ganglion  of  the  sympathetic  of  the  left 
side;  (2)  the  inferior  cervical  cardiac  branch  of  the  left 
pneumogastric  nerve.  Look  for  both  of  these  nerves  upon 
the  aortic  arch.  They  will  be  found  crossing  it  to  the  left 
of  the  phrenic  nerve,  between  it  and  the  pneumogastric  nerve. 
The  cardiac  branch  from  the  left  pneumogastric  nerve  is  the 
smaller  of  the  two,  and  as  a  general  rule  it  lies  nearer  the 
phrenic  nerve  than  the  other. 

The  superficial  cardiac  plexus  into  which  these  nerves 
may  be  traced  lies  in  the  concavity  of  the  aortic  arch,  and 
upon  the  bifurcation  of  the  pulmonary  artery.  At  the  point 
of  junction  of  the  nerves  the  minute  ganglion  of  Wrisberg  may 
be  discovered.  The  manner  in  which  this  plexus  is  distri- 
buted to  the  heart  will  be  afterwards  noted  :  in  the  meantime, 
observe  that  it  gives  some  fine  offsets  to  the  left  anterior 
pulmonary  plexus. 

Dissection. — The  pericardium  should  now  be  cleaned.  In  removing  the 
loose  areolar  tissue  from  its  anterior  surface  two  ligamentous  bands  which 
connect  it  to  the  posterior  aspect  of  the  sternum  will  be  observed.  Of 
these,  one — the  inferior  stemo-pericardiac  ligament — binds  it  to  the  ensi- 
form  cartilage,  whilst  the  other — the  superior  sterno-pericardiac  ligament — 
connects  it  with  the  manubrium  sterni,  and  comes  into  relation  with  the 
pretracheal  layer  of  the  deep  cervical  fascia.  The  upper  surface  of  the 
diaphragm  should  be  carefully  cleaned  at  the  same  time,  in  order  that  its 
relation  to  the  pericardium  may  be  studied. 

Pericardium. — The  pericardium  is  a  fibro-serous  sac  which 
loosely  envelops  the  heart.  It  is  placed  in  the  middle  sub- 
division of  the  mediastinal  space,  and  presents  a  somewhat 
conical  form.  By  its  base  it  rests  chiefly  upon  the  central 
tendinous  part  of  the  diaphragm,  but  beyond  the  limits  of 
this  it  encroaches,  to  some  extent,  upon  the  muscular  portion. 
More  especially  is  this  the  case  on  the  left  side.  Except  at 
one  point,  no  difficulty  will  be  experienced  in  separating  the 
pericardium  from  the  diaphragm.  The  two  are  simply  bound 
together  by  some  intervening  areolar  tissue.  Towards  the 
middle  line,  however,  it  will  be  found  over  a  small  area  to  be 
inseparably  blended  with  the  central  tendon.  It  is  important 
to  recognise  the  abdominal  viscera  which  stand  in  relation  to 
the  base  of  the  pericardium.  It  is  placed,  for  the  greater 
part  of  its  extent,  over  the  upper  surface  of  the  liver,  the 
diaphragm  alone  intervening ;  but  in  front,  a  small  part  cor- 
responding to  the  apex  of  the  heart  projects  beyond  the  area 
of  the  liver  and  comes  to  lie  over  the  stomach.     The  upper 


3^ 


THORAX 


narrow  part  of  the  pericardium  will  be  noticed  to  close  upon 
certain  of  the  great  vessels  that  issue  from  the  base  of  the 
heart.  Upo?i  each  side  the  pericardium  is  adapted  to  the 
concave  part  of  the  mediastinal  surface  of  the  lung.  It  is 
clothed  by  the  mediastinal  pleura,  and  has  in  relation  to  it 


Common  carotid 

artery 

Subclavian 


Mouth  of  superior 

vena  cava 

Right  pulmonary 

veins 


Common  carotid  artery 
Internal  jugular  vein 
Recurrent  laryngeal  nerve 
Subclavian  artery 

Subclavian  vein 

Left  innominate  vein 
Vagus  nerve 

Phrenic  nerve 


Left  pulmonary  artery 

Left  bronchus 

Right  pulmonary  artery 

Left  pulmonary  veins 


Interior  of  pericardium 
Phrenic  nerve 


Fig.  i 8. — The  Pericardium  and  Great  Vessels  of  the  Heart.  The  thoracic 
organs  were  hardened  in  situ  by  formalin  injection.  The  pericardium 
having  been  opened  by  the  removal  of  its  anterior  wall,  the  great  vessels 
were  divided  and  the  heart  removed. 

the  phrenic  nerve  and  the  arteria  comes  nervi  phrenici.  In 
front,  very  important  relations  have  to  be  studied.  It  lies 
behind  the  sternum  and  costal  cartilages,  and  is  for  the  most 
part  separated  from  these  by  the  two  pleural  sacs,  and  by  the 
anterior  thin  margins  of  the  lungs.  Below  the  level  of  the 
sternal  end  of  the  fourth  costal  cartilage,  however,  owing  to 


THORACIC  CAVITY  37 

the  left  pleura  retreating  somewhat  to  the  left,  a  small  area 
of  the  anterior  surface  of  the  pericardium,  as  a  general  rule, 
comes  into  direct  relation  with  the  chest  wall.  The  extent x 
of  this  area,  as  we  have  already  seen,  is  variable.  Behind, 
the  pericardium  forms  the  anterior  wall  of  the  posterior 
mediastinum,  and  is  in  relation  to  the  contents  of  this  space. 
Its  relation  to  the  oesophagus  is  especially  intimate. 

Fibrous  Pericardium. — When  the  pericardium  is  denuded 
of  the  loose  areolar  tissue  which  surrounds  it  and  binds  it  to 
adjacent  structures,  the  strong  dense  character  of  the  fibrous 
membrane  which  forms  its  outer  layer  will  be  seen.  This 
fibrous  layer  is  pierced  by  the  various  vessels  which  pass  to 
and  from  the  heart,  and  is  prolonged  upon  the  walls  of  these 
vessels  in  the  form  of  tubular  investments  which  gradually 
become  lost  upon  their  coats.  The  only  vessel  which  fails  to 
receive  such  a  prolongation  is  the  inferior  vena  cava,  and 
this  is  due  to  the  fact  that  this  vein  pierces  the  pericardium 
where  it  rests  on  the  diaphragm,  and  can,  therefore,  hardly 
be  said  to  have  any  intra -thoracic  course  outside  the  peri- 
cardium. 

The  entire  length  of  the  pulmonary  artery  and  of  the 
ascending  aorta  are  enclosed  within  the  fibrous  sac  of  the 
pericardium.  Portions  also  of  the  superior  vena  cava  and 
the  four  pulmonary  veins  are  contained  within  the  fibrous 
pericardium. 

Dissection. — The  pericardium  may  be  opened  by  means  of  a  crucial 
incision,  viz. — (1)  a  longitudinal  incision  along  the  middle  line  of  the 
body  from  the  point  where  it  blends  with  the  sheath  of  the  aorta  down- 
wards to  the  diaphragm  ;  (2)  a  transverse  cut,  extending  from  the  middle 
of  the  root  of  one  lung  to  a  similar  point  on  the  opposite  side. 

Serous  Layer  of  the  Pericardium. — The  internal  serous 
layer  is  now  exposed.  This  layer,  which  forms  a  completely 
closed  sac,  lines  the  entire  inner  surface  of  the  fibrous  peri- 
cardium, and  is  reflected  from  this,  upon  the  vessels  which 
pierce  the  fibrous  layer,  on  to  the  surface  of  the  heart.  It 
gives  a  smooth,  polished  appearance  to  the  heart  and  to  the 
interior  of  the  pericardial  sac.  The  lining  part  of  the  serous 
layer  is  termed  the  parietal  portion ;  the  investing  portion 
which  covers  the  heart  is  called  the  visceral  part  or  the  epi- 


1  The  importance  of  recognising  this  bare  area  of  the  pericardium  will  be 
understood  when  it  is  remembered  that  it  is  here  that  the  surgeon  taps  the 
cavity  of  the  sac  when  it  is  distended  with  fluid. 


38  THORAX 

cardium.  The  great  vessels  in  connection  with  the  heart,  as 
they  lie  within  the  fibrous  pericardium,  also  receive  more  or 
less  complete  coverings  from  the  serous  layer.  The  two 
arteries,  viz.,  the  pulmonary  artery  and  the  aorta,  are  com- 
pletely surrounded  by  a  single  tubular  sheath  which  is 
common  to  both.  This  investment  only  leaves  uncovered 
the  surfaces  of  these  vessels  which  are  in  apposition  with 
each  other — a  fact  which  can  readily  be  demonstrated  by 
passing  the  forefinger  behind  them.  The  term  sinus  trans- 
versus  pericardii  is  given  to  the  passage  through  which  the 
finger  goes.  It  intervenes  between  the  two  arteries  in  front, 
and  the  auricular  part  of  the  heart  behind. 

In  the  case  of  the  veins,  the  covering  which  they  receive 
from  the  serous  pericardium  is  not  so  complete.  They  are 
covered  in  front  and  on  each  side,  whilst  posteriorly  they  are 
bare  and  in  contact  with  the  fibrous  layer  of  the  sac.  The 
superior  vena  cava,  which  lies  immediately  to  the  right  of  the 
ascending  part  of  the  aorta,  is  a  good  example  of  this.  The 
lower  half  of  this  vein  is  enclosed  within  the  fibrous  sac,  but 
only  two-thirds  of  its  circumference  has  a  serous  covering. 
The  inferior  vena  cava,  which  pierces  the  base  of  the  peri- 
cardium, and  at  once  opens  into  the  right  auricle  of  the  heart, 
receives  a  very  small  investment. 

When  the  apex  of  the  heart  is  drawn  forwards  and  up- 
wards, a  deep,  blind  recess  of  the  serous  pericardium  will  be 
seen,  passing  upwards  behind  it,  between  the  openings  of  the 
pulmonary  veins  of  opposite  sides  into  the  back  of  the  left 
auricle.  This  recess  lies  between  the  posterior  or  auricular 
surface  of  the  heart  and  the  posterior  wall  of  the  fibrous  peri- 
cardium, and  is  called  the  oblique  sinus. 

Lastly,  separate  the  left  pulmonary  artery  from  the  upper 
of  the  two  left  pulmonary  veins,  as  they  lie  within  the  fibrous 
pericardium.  Stretching  across  the  interval  between  them 
will  be  seen  a  prominent  semilunar  fold  of  the  serous  peri- 
cardium. This  is  the  "vestigial fold  of  Mars hall.''''  It  contains 
between  its  two  layers  a  minute  fibrous  band  (ligamentum 
cavae  sinistra^),  the  remnant  of  the  left  superior  vena  cava  of 
the  embryo. 

Remains  of  the  Thymus. — The  thymus  gland,  which  is  a 
large  and  conspicuous  object  in  the  superior  and  middle 
portions  of  the  mediastinum  of  the  foetus  and  young  child,  is 
only   represented    in    the    adult    by    two   slender  elongated 


THORACIC  CAVITY  39 

bodies  placed  in  the  fore  part  of  the  superior  mediastinum 
in  front  of  the  aortic  arch  and  the  left  innominate  vein.  A 
few  thymic  branches  from  the  internal  mammary  artery  enter  the 
wasted  remains  of  the  gland,  and  some  small  veins  pass  from 
it  and  join  the  subjacent  left  innominate  venous  trunk. 

Dissection. — Remove  the  thymus,  and  dissect  out  the  two  innominate 
veins  and  the  superior  vena  cava.  The  left  innominate  vein  will  be  seen 
crossing  the  superior  mediastinum  from  left  to  right.  The  short  right 
innominate  vein  is  placed  in  the  upper  and  right  part  of  the  superior 
mediastinum.  The  union  of  these  two  trunks  forms  the  vena  cava  superior. 
The  tributaries  which  enter  these  veins  must  also  be  secured.  One,  the 
left  superior  intercostal  vein,  ascends  upon  the  aortic  arch  to  reach  the  left 
innominate. 

Innominate  Veins. — The  innominate  vein  of  each  side  is 
formed  behind  the  sternal  end  of  the  clavicle  by  the  union  of 
the  subclavian  and  internal  jugular  veins.  Behind  the  lower 
part  of  the  -junction  of  the  first  costal  cartilage  of  the  right 
side  with  the  sternum,  they  unite  to  form  the  superior  vena 
cava. 

The  right  innominate  vein  (vena  anonym  a  dextra)  is  short. 
It  is  not  more  than  one  inch  in  length,  and  it  has  a  nearly 
vertical  course  from  above  downwards.  It  is  covered  on  its 
outer  and  anterior  aspects  by  the  right  mediastinal  pleura,  and 
the  phrenic  nerve  is  applied  to  its  outer  side.  The  upper 
part  of  the  innominate  artery  lies  to  its  inner  or  left  side. 

The  left  innominate  vein  (vena  anonym  a  sinistra)  is  much 
longer  than  the  right  vein,  and  has  an  oblique  course  from 
the  left  downwards  and  to  the  right.  It  is  placed  behind 
the  manubrium  sterni  and  the  remains  of  the  thymus  gland, 
and  crosses  in  front  of  the  three  great  arteries  which  spring 
from  the  aortic  arch  and  also  in  front  of  the  left  vagus  and 
left  phrenic  nerves.  In'  the  greater  part  of  its  extent  it  is 
covered  by  the  left  mediastinal  pleura. 

The  innominate  vein  of  each  side  receives  the  following 
tributaries : — 

1.  The  vertebral  vein. 

2.  The  inferior  thyroid  vein. 

3.  The   vein  which  drains  the  blood  from  the  first  or  highest  inter- 

costal space. 

4.  The  internal  mammary  vein. 

The  left  innominate  vein  in  addition  receives  the  left 
superior  intercostal  vein,  and  some  small  venous  twigs  from 
the  thymus  gland.      The  left  superior  intercostal  veifi  is  formed 


40  THORAX 

by  the  union  of  the  veins  from  the  second  and  third  inter- 
costal spaces.  It  crosses  the  arch  of  the  aorta,  and  is  of 
interest  in  so  far  that  its  upper  part  represents  the  upper 
pervious  portion  of  the  occluded  left  superior  vena  cava  of 
the  embryo. 

Vena  Cava  Superior. — This  great  vein  is  formed  behind 
the  first  costo-sternal  junction  of  the  right  side  by  the  union 
of  the  two  innominate  veins.  From  this  it  proceeds  down- 
wards, and  it  opens  into  the  upper  and  back  part  of  the  right 
auricle  of  the  heart  at  the  level  of  the  upper  border  of  the 
third  costal  cartilage  of  the  right  side.  It  is  three  inches 
long,  and  shows  very  different  relations  in  its  upper  and  lower 
parts.  In  the  upper  half  of  its  course  it  lies  in  the  superior 
mediastinum  (Fig.  38,  p.  68).  On  the  right  side  it  is  clothed 
by  the  mediastinal  pleura,  and  has  the  phrenic  nerve  in  con- 
tact with  it  j  on  the  left  side  it  is  in  relation  to  the  innominate 
artery.  In  the  lower  half 'of  its  course  it  is  enclosed  within 
the  fibrous  pericardium,  and  is  placed  in  the  middle  media- 
stinum. The  serous  pericardium  covers  it  in  front  and 
laterally,  whilst  immediately  to  its  left  side  is  the  ascending 
aorta.  This  portion  of  the  superior  vena  cava  lies  in  front  of 
the  right  bronchus,  the  right  pulmonary  artery,  and  the  upper 
right  pulmonary  vein  (Fig.  39,  p.  69). 

The  ve?ia  azygos  ??iajor  is  the  only  large  tributary  which 
joins  the  superior  vena  cava.  It  comes  forwards  above  the 
right  bronchus,  and  enters  the  vena  cava  immediately  above 
the  point  where  it  pierces  the  pericardium.  Minute  peri- 
cardiac and  mediastinal  veins  also  pour  their  blood  into  it. 

Inferior  Vena  Cava. — This  is  a  larger  vessel  than  the 
superior  vein  of  the  same  name.  It  enters  the  thorax  by 
piercing  the  central  tendon  of  the  diaphragm.  It  can  hardly 
be  said  to  have  any  course  within  the  thorax,  seeing  that  it 
immediately  passes  through  the  base  of  the  pericardium,  and 
opens  into  the  lower  and  back  part  of  the  right  auricle  of 
the  heart. 

Heart. — The  heart  is  a  hollow  organ  with  muscular  walls 
and  somewhat  conical  in  shape.  It  is  placed  obliquely 
within  the  middle  mediastinum,  so  that  its  basal  portion 
(basis  cordis)  is  directed  backwards,  and  slightly  to  the 
right,  while  its  pointed  apex  looks  downwards,  forwards,  and 
to  the  left.  But  it  is  also  placed  unsymmetrically  within  the 
chest  cavity.      In  other  words,   it  projects  more  to  the  left 


THORACIC  CAVITY 


4i 


than  to  the  right ;  and  in  cases  where  the  frozen  body  is 
divided  accurately  in  the  mesial  plane,  it  is  found  that  about 
one-third  of  the  organ  is  in  the  right,  and  about  two-thirds  in 
the  left  half  of  the  thoracic  cavity  (Fig.  19). 

General  Relations  of  the  Heart. — The  base  or  posterior 
surface  of  the  heart  is  placed  in  front  of  the  middle  portion  of 
the  dorsal  segment  of  the  vertebral  column.  Four  dorsal 
vertebrae  lie  above  it,  and  four  below  it,  whilst  the  intermediate 
four  (viz.,  the  5th,  6th,  7th,  and  8th)  lie  behind  it.  The 
apex  approaches  the  anterior  wall  of  the  thorax,  and  in  life 
will  be  felt  beating  in  the  fifth  intercostal  space  of  the 
left  side,  one  and  a  half 
inches  below  the  nipple,  and 
three  and  a  half  inches  from 
the  middle  line.  The  inferior 
surface  (facies  diaphragm atica), 
which  is  flattened,  and  f 
looks  downwards,  rests  upon 
the  diaphragm  —  the  floor  of 
the  pericardium  alone  inter- 
vening. Immediately  below 
the  cardiac  area  of  the  dia- 
phragm is  the  upper  surface 
of  the  liver,  and  in  front  and 
to  the-  left  a  small  piece  of 
the  stomach.  The  antero- 
superior    surface    (facies     ster- 

nalis)  of  the  heart  looks  upwards  as  well  as  forwards,  and  lies 
behind  the  greater  part  of  the  gladiolus  of  the  sternum  and 
the  third,  fourth,  fifth,  and  sixth  cartilages  of  both  sides. 
Owing  to  the  greater  projection  of  the  organ  to  the  left,  only 
a  small  portion  of  the  inner  ends  of  these  cartilages  lies  in 
front  of  the  heart  on  the  right  side.  A  much  larger  area  of  the 
antero-superior  cardiac  surface  lies  behind  the  left  costal  carti- 
lages. Indeed,  behind  the  fourth  and  fifth  costal  cartilages  the 
left  margin  of  the  heart  approaches  closely  to  the  junction  be- 
tween the  osseous  and  cartilaginous  portions  of  these  costal 
arches.  The  pleural  sacs  and  the  anterior  thin  margins  of  the 
lungs  intervene  between  the  heart  enclosed  within  the  peri- 
cardium and  the  anterior  wall  of  the  thorax.  A  small  portion  of 
the  pericardium  in  the  lower  part  of  the  anterior  mediastinum  is 
in  direct  relation  to  the  triangularis  sterni  muscle  as  it  covers  the 


Fig.  19. — The  vertical  line  drawn 
through  the  heart  represents  the 
mesial  plane.      (From  Braune. ) 


42 


THORAX 


deep  surface  of  the  sternum,  and  the  inner  extremities  of  the 
fifth  and  sixth  costal  cartilages  of  the  left  side.  A  wider  area 
at  the  same  level,  owing  to  the  incisura  cardiaca  in  the  anterior 
margin  of  the  left  lung,  is  uncovered  by  the  lung  (Fig.  8,  p.  18). 
This  area  may  be  mapped  out  on  the  chest  wall  by  drawing  a 


Fig.  20. — The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 
Thoracic  Wall.      (Young  and  Robinson.) 

Af.   Mitral  orifice. 

P.   Pulmonary  orifice. 
RA.  Right  auricle. 
RV.  Right  ventricle. 
SVc.  Superior  vena  cava. 

T.   Tricuspid  orifice. 

vertical  line  along  the  middle  line  of  the  sternum,  from  the 
level  of  the  inner  extremities  of  the  fourth  costal  cartilages  to 
the  lower  end  of  the  gladiolus,  and  by  carrying  two  other 
lines,  from  its  extremities,  outwards  so  as  to  meet  at  a  point 
over  the  apex  beat  of  the  heart.      On  either  side,  the  heart 


I  to  VII. 

Costal  cartilages 

A. 

Aortic  orifice. 

Ao. 

Aorta. 

C. 

Clavicle. 

LA. 

Left  auricle. 

LV. 

Left  ventricle. 

THORACIC  CAVITY 


43 


and  pericardium  is  supported  by  the  mediastinal  pleura  and 
the  inner  surface  of  the  lung. 

The  heart  lies  free  within  the  sac  formed  by  the  peri- 
cardium, except  where  it  is  attached  by  the  great  vessels 
which  are  connected  with  its  basal  portion.  Its  position  is 
influenced,  to  a  certain  extent,  by  the  position  of  the  body. 


Right 

innominate  vein 

Innominate  artery 


Superior  vena  cava 


Serous 
pericardium 


Right  appendix 


Auriculo- 

ventricular 

furrow 


Marginal  branch 
of  right  coronar 
artery 

Right  ventricle 


Left  common  carotid 
Left  subclavian 

Left  innominate  vein 

Aortic  arch 
Ligamentum  arteriosum 

Left  pulmonary  artery 
Pulmonary  artery 

Left  appendix 
Infundibulum 


Anterior  interven- 
tricular furrow 
with  corresponding 
branch  of  left  coro- 
nary artery 

Left  ventricle 


Apex  of  heart 


Fig.  2i.— Anterior  or  Sternal  Aspect  of  the  Heart. 

External  Configuration  of  the  Heart.  —  In  studying  the 
form  and  appearance  of  the  heart,  the  dissector  will  find  it 
advantageous  to  refer  to  a  specimen  which  has  been  hardened 
in  situ  by  formalin  injection. 

The  interior  of  the  heart  is  divided  by  an  internal, 
obliquely  placed  partition  into  a  right  and  a  left  cavity. 
Further,  each  of  these  is  still  further  subdivided  into  an 
upper  auricular  and  a  lower  ve?iiricular  cha?nber,  which   com- 


44 


THORAX 


municate  freely  with  each  other  through  a  wide  auricula- 
ventricular  ope?ii?ig.  The  right  and  the  left  cavities  of  the 
heart,  however,  are  completely  shut  off  from  each  other. 

On  the  exterior  of  the  heart  there  are  markings  which 
indicate  this  internal  subdivision,  and  enable  us  to  map  out 
with  the  greatest  accuracy  the  walls  of  the  four  chambers. 
Thus   encircling    the  heart  nearer   the   base  than   the  apex, 


Right  auriculo 
ventricular  opening 


Superior  vena  cava 


Reflection  of  serous  pericardium 


Right  appendix 
Interauricular  furrow 
Left  auricle 

appendix 


Crista  terminally 

Fossa  ovalis 
Eustachian  valve 

Inferior  vena  cava 


eft  auriculo- 
ventricular  opening 


Coronary  sinus 


Fig.  22. — The  Anterior  Aspect  ot  the  Auricular  Part  of  the  Heart.  The 
auricles  have  been  removed  from  the  ventricles.  The  ventricular  portion 
of  the  same  heart  is  depicted  in  Fig.  25.  The  specimen  was  hardened 
in  situ. 

and  in  a  direction  transverse  to  its  long  axis,  is  a  deep 
furrow  which  is  continuous  all  the  way  round,  except  in  front, 
where  it  is  interrupted  by  the  root  of  the  pulmonary  artery. 
This  is  the  auriculo-ventricular  groove  (sulcus  coronarius).  It 
intervenes  between  the  auricles  which  lie  behind  it  and  the 
ventricles  which  are  placed  in  front  and,  to  some  extent,  below 
it.  In  the  undissected  heart,  with  the  epicardium  in 
position,  the  depth  of  this  furrow  is  greatly  obscured,  from 


THORACIC  CAVITY 


45 


the  fact  that  it  lodges  some  large  blood  vessels  and  a  certain 
amount  of  fat. 

The  Auricular  Part  of  the  heart  stands  in  marked  con- 
trast with  the  firm  ventricular  portion.  Its  walls  are  thin 
and  flaccid,  and,  in  the  heart  which  has  not  been  hardened 
by  formalin,  they  are  collapsed,  so  that  it  is  difficult  to 
realise  the  shape  of  this  portion  of  the  organ.  It  is  crescentic 
in  form.  The  chief  bulk  of  it  is  placed  behind,  but  it  sends 
upwards  and  forwards  two  processes  or  cornua,  termed  the 
auricular  appendices.  A  deep  concavity  or  hollow  is  thus 
produced,  in  which  lie  the  two  great  arterial  trunks  which 
spring  from  the  ventricles,  viz.,  the  pulmonary  artery  in  front 
and  the  aorta  behind.  These 
great  vessels  are,  as  it  were, 
clasped  between  the  auricular 
appendices. 

On  referring  to  the  hardened 
organ   it  will   be  seen  that  the 
whole  of  the  posterior  surface  or 
base  of  the  heart  is  formed  by 
the  auricles.     The  surface  thus 
constituted   is  somewhat   quad- 
rangular in  outline.     Above,  it 
is  in  intimate  relation  to  the  two 
pulmonary  arteries  as  they  run 
to  the  right  and  to  the  left  to 
enter  the  pulmonary  roots  ;  be- 
low, it  is  limited  by  that  part  of 
the    auriculo-ventricular    groove 
which  is  occupied  by  the  coronary  sinus.      A  groove  which 
runs  downwards  on  the  right  auricle  from  the  front  of  the 
opening  of  the  superior  vena  cava  to  the  right  of  the  opening 
of  the   inferior   vena   cava   may  be   taken   as   bounding   the 
posterior    auricular    surface    on    the    right.       This   furrow  is 
termed     the    sulcus    termi?ialis,    and    it    has     an     interesting 
embryological   significance.       The   entrance   of   the   two   left 
pulmonary  veins  into   the   left  auricle  form   the  left  limit  of 
the    posterior   auricular    surface    of   the  heart.       By  far   the 
greater  part  of   this   posterior  surface  is  formed  by  the  left 
auricle,   and  the  exact    proportions  which  the  two   auricular 
chambers    contribute    to   this   surface   are    indicated   on  the 
hardened  organ  by  a  faint  groove  termed  the   interauricular 


Fig.  23.  — Transverse  section 
through  the  Auricular  Part  of 
the  Heart  of  an  Ox. 

R.A.  Right  auricle. 

L.A.  Left  auricle. 

P.  Pulmonary  artery. 

A.  Aorta. 


46 


THORAX 


furrow,  which  pursues  a  vertical  course  immediately  to  the 
left  of  the  openings  of  the  two  venae  cavae.  This  furrow 
indicates  the  posterior  attachment  of  the  interauricular 
septum. 

Each  auricle  is  composed  of  a  roomy  capacious  posterior 


Left  common  carotid 

Aorta 
Ligamentum  arteriosum 

Left  pulmonary  artery 


Reflection  of  serous 
pericardium 


Left 

pulmonary 
veins 


Left  auricle 

Oblique  vein 
Margo  obtusus 

Auriculo- 
ventricular  groove'""|| 

Coronary  sinus. 

Inferior  surface 
ventricular  part 
of  heart 


Innominate  artery 
Right  innominate 
vein 


Vena  azygos 
major 
Superior 
vena  cava 

Right  pulmonary 
artery 

Right  pulmonary 


Sulcus 
terminalis 

Right 
pulmonary  vein 


Interauricular 
sulcus 

Right  auricle 


Inferior  vena 
cava 


Fig.  24. — Posterior  or  Basal  Aspect  of  a  Heart  hardened  in  situ  by 
formalin  injection. 


part  into  which  the  veins  open  and  into  which  the  blood 
flows,  termed  the  atrium,  and  a  more  or  less  pointed  pro- 
jection which  springs  from  the  upper  and  fore  part  of  the 
atrium.      This  prolongation  is  the  auricular  appendix. 

The  superior  vena  cava  will  be  seen  to  open  into  the 
upper  part  of  the  atrium  of  the  right  auricle ;  the  inferior 
vena  cava  opens  into   the   lower   part   of  the  same   atrium. 


THORACIC  CAVITY 


47 


Between  these  two  openings,  and  immediately  to  the  left  of 
the  interauricular  furrow,  the  two  right  pulmonary  veins 
pierce  the  posterior  wall  of  the  atrium  of  the  left  auricle  ;  the 
left  pulmonary  veins  open  into  the  same  atrium  at  the  left 
limit  of  the  posterior  surface  of  the  heart. 

The  Ventricular  Part  of  the  heart  is  firm  to  the  touch 
and  possesses  thick  fleshy  walls.      It  is  conical  in  form.      Its 


Left 

pulmonary 

artery 


Pulmonary  artery 

Anterior  inter- 
ventricular branch 

Left  posterior  sinus 
of  Valsal 


Left  coronary 
artery 


Aortic  cusp  of 
mitral  valve 


Posterior  cusp-~J 


Ligamentum  arteriosum 

Pulmonary  artery 
-Aorta 


—Right  pulmonary  artery 


Infundibulum 


Right  coronary  artery 

Right  posterior  sinus 
of  Valsalva 


\^\lu\         Infundibular  cusp 
JliK       of  tricuspid  valve 

Marginal  cusp 
Septal  cusp 


Marginal  branch 
Inferior  interventricular  branch 


Fig.  25. — The  Base  of  the  Ventricular  Part  of  the  Heart  from  which  the 
Auricles  have  been  removed.  The  detached  auricles  are  depicted 
in  Fig.  22.      The  specimen  was  hardened  in  situ. 


apex  corresponds  to  the  apex  of  the  heart ;  whilst  its  base 
is  connected  behind  with  the  two  atria  of  the  auricular  part 
of  the  heart,  and  gives  origin  above  and  in  front  of  these, 
and  in  the  interval  between  the  auricular  appendices,  to  the 
two  great  arteries  which  conduct  the  blood  from  the  ventri- 
cular chambers,  viz.,  the  pulmonary  artery  in  front,  and  the 
aorta  behind. 

In  addition   to  the  base  and  apex,    the   ventricular   part 


48  THORAX 

of  the  heart  presents  two  borders  and  two  surfaces.  One 
border  is  long  and  sharp,  and  runs  from  right  to  Jeft,  from 
the  base  to  the  apex.  It  occupies  that  part  of  the  basal 
portion  of  the  pericardium  which  lies  in  the  narrow  interval 
between  the  diaphragm  and  the  anterior  wall  of  the  chest ; 
it  is  called  the  a?iterior  border  or  the  margo  acutus.  The  left 
border  or  margo  obtusus  is  short,  thick,  and  rounded. 

The  antero-superior  surface  (facies  sternalis)  of  the  ventricular 
part  of  the  heart  is  full  and  convex,  and  is  traversed  by  a 
groove  which  begins  above  at  the  auriculo-ventricular  furrow 
immediately  to  the  left  of  the  origin  of  the  pulmonary  artery, 
and  proceeds  forwards  and  downwards  towards  the  sharp 
margin,  which  it  reaches  a  little  to  the  right  of  the  apex. 
This  groove  is  the  anterior  interventricular  furrow  (sulcus 
longitudinalis  anterior),  and  it  is  placed  much  nearer  to  the 
left  margin  than  to  the  sharp  anterior  margin  of  the  heart 
(Fig.  21,  p.  43).  The  i?iferior  surface  (facies  diaphragmatica) 
is  flattened  and  traversed  by  a  similar  groove  (Fig.  24, 
p.  46),  the  inferior  interventricular  furrow  (sulcus  longi- 
tudinalis posterior).  This  joins  the  anterior  groove  below, 
round  the  anterior  sharp  margin  of  the  heart.  These 
grooves  are  occupied  by  vessels  and  lodge  a  little  fat. 
They  indicate  on  the  surface  the  attachments  of  the  inter- 
ventricular septum,  and  therefore  the  extent  of  the  walls 
of  the  two  cavities.  Roughly  speaking,  two-thirds  of  the 
antero-superior  surface,  the  margo  acutus,  and  rather  more 
than  one-third  of  the  inferior  surface,  belong  to  the  right 
ventricle ;  whilst  one-third  of  the  antero-superior  surface,  the 
margo  obtusus,  the  apex  of  the  heart,  and  rather  less  than 
two-thirds  of  the  inferior  surface,  belong  to  the  left  ventricle. 
On  the  antero-superior  surface  of  the  heart  a  bulging  of  the 
wall  of  the  right  ventricle  will  be  noticed  in  its  upper  and 
front  part.  This  is  termed  the  infundibulum  or  conus 
arteriosus  (Fig.  21,  p.  43).  From  its  summit  the  pulmonary 
artery  takes  origin. 

Dissection. — The  vessels  and  nerves  which  are  distributed  to  the 
substance  of  the  heart  may  now  be  dissected.  The  main  trunks  occupy 
the  furrows,  and  can  be  exposed  by  ronoving  the  epicardium  and  the 
soft  fat  which  is  generally  placed  around  them.  In  a  young  subject, 
where  the  fat  is  scanty  and  the  vessels  well  injected,  very  little  dissection 
is  required.  The  nerves  are  exceedingly  delicate  and  are  derived  from 
the  cardiac  plexus.  It  is  seldom  that  they  can  be  satisfactorily  displayed 
in  an  ordinary  dissecting-room  subject. 


THORACIC  CAVITY  49 

Coronary  Arteries  (Fig.  25,  p.  47).  —  These  are  the 
nutrient  vessels  of  the  heart.  They  are  two  in  number, 
and  spring  from  the  root  of  the  ascending  aorta.  It  is 
here,  therefore,  that  they  must  in  the  first  instance  be  sought, 
by  dissecting  deeply  in  the  auriculo-ventricular  furrow.  The 
left  coronary  artery  (arteria  coronaria  sinistra)  springs  from  the 
left  posterior  sinus  of  Valsalva,1  and  proceeds  outwards 
behind  the  pulmonary  artery.  It  winds  round  the  left  side 
of  the  left  auriculo-ventricular  opening  (ramus  circumflexus), 
and  ends  on  the  inferior  aspect  of  the  heart.  Throughout 
its  entire  course  it  lies  in  the  auriculo-ventricular  furrow.  It 
gives  off  numerous  twigs  to  the  left  auricle  and  left  ventricle, 
and  one  large  branch  will  be  observed  to  pass  downwards 
in  the  anterior  interventricular  groove  towards  the  apex  of 
the  heart  (ramus  descendens). 

The  right  coronary  artery  (arteria  coronaria  dextra)  arises 
from  the  anterior  sinus  of  Valsalva,  and  winds  round  the  right 
side  of  the  right  auriculo-ventricular  opening  in  the  auriculo- 
ventricular  groove  to  reach  the  inferior  aspect  of  the  heart, 
where  it  ends  near  the  termination  of  the  artery  of  the  left  side. 
An  arterial  circle  is  thus  formed,  which  embraces  the  heart  in 
the  auriculo-ventricular  groove.  The  right  coronary  artery 
gives  off  two  large  branches.  Of  these,  one  passes  towards 
the  apex  upon  the  sharp  margin  of  the  heart,  whilst  the 
second  and  larger  proceeds  towards  the  apex  in  the  inferior 
interventricular  groove  (ramus  descendens).  It  also  supplies 
numerous  smaller  twigs  to  the  right  ventricle  and  right 
auricle. 

Cardiac  Veins  (vena?  cordis). — Take  hold  of  the  heart  by 
the  apex  and  pull  it  upwards,  so  as  to  bring  into  view  its 
inferior  surface.  In  the  groove  between  the  left  ventricle  and 
left  auricle — the  coronary  sinus  (sinus  coronarius) — a  short  wide 
venous  channel  will  be  seen  (Fig.  24,  p.  46).  Open  it  with  the 
scissors  along  its  whole  length.  By  one  extremity  it  opens  into 
the  right  auricle,  whilst  by  its  other  end  it  becomes  continuous 
with  the  great  cardiac  vein,  and  the  point  of  junction  is  marked 
by  a  valve  of  two  segments.  Several  posterior  cardiac  veins 
from  the  inferior  aspect  of  the  ventricles  also  open  into  this 


1  The  three  sinuses  of  Valsalva  are  three  bulgings  of  the  wall  of  the 
aortic  root.  One  is  on  the  front,  and  the  other  two  on  the  back  of  the 
vessel. 

VOL,   ll       1 


5° 


THORAX 


sinus,  and  each  orifice  is  guarded  by  a  distinct  valve.  Of 
these,  one  much  larger  than  the  others,  and  called  the  middle 
cardiac  vein  (vena  cordis  media),  occupies  the  inferior  inter- 
ventricular groove.  The  right  or  small  cardiac  vein  (vena  cordis 
parva)  likewise  joins  the  coronary  sinus  close  to  its  termination. 
It  occupies  that  part  of  the  auriculo-ventricular  furrow  which, 
on  the  posterior  surface  of  the  heart,  intervenes  between  the 
right  auricle  and  right  ventricle.  Lastly,  the  oblique  veifi  of 
Marshall  (vena  obliqua  atrii  sinistra)  from  the  back  of  the  left 
auricle  opens  into  the  sinus  close  to  the  point  where  it  joins 

Oblique  vein 
of  .Marshall 


Fig.  26. — The  Coronary  System  of  Veins  on  the  Surface  of  the 
Heart.      (Diagram. ) 

the  right  auricle.  The  orifice  of  this  vein  is  devoid  of  a  valve. 
The  oblique  vein  is  very  minute,  and  would  not  deserve 
special  mention,  were  it  not  that  it  represents  the  lower 
pervious  part  of  the  obliterated  left  superior  vena  cava  of  the 
embryo. 

The  great  cardiac  vein  (vena  cordis  magna)  begins  upon  the 
antero-superior  aspect  of  the  heart  at  the  apex.  It  ascends 
in  the  anterior  interventricular  groove  to  the  auriculo-ventricular 
furrow,  in  which  it  turns  round  the  left  margin  of  the  heart  to 
join  the  coronary  sinus.  On  its  way  it  is  joined  by  numerous 
veins  from  the  surface  of  both  the  ventricular  and  auricular 
parts  of  the  heart. 


THORACIC  CAVITY  51 

The  anterior  cardiac  veins  will  be  seen  on  the  front  surface 
of  the  right  ventricle.  They  open  directly  into  the  right 
auricle. 

But,  in  addition  to  those  veins  which  appear  upon  the 
surface,  there  are  minute  vessels  in  the  substance  of  the  heart 
— the  vena  Thebesii  or  vena  i?iini??icz  cordis — the  orifices  of  which 
will  be  recognised,  when  the  right  auricle  is  opened,  as  the 
foramina  Thebesii. 

The  cardiac  veins,  therefore,  which  drain  the  blood  from 
the  heart,  do  not  correspond  with  the  arteries.  The  following 
table  expresses  the  arrangement  in  a  brief  form  : 

f  Great  cardiac  vein.  I  opening  into 

Posterior  cardiac  veins.  J  coronary 

Upon  the  surface]    Right  cardiac  vein.  I  sinus 

of  the  heart.  Oblique  vein.  I 

.  .  , .  .  f        Opening  into 

Anterior  cardiac  veins.  j        right  auricle# 

In  the  substance   /  Ven^  Thebesii.  /        Opening  into 

of  the  heart.        ^  I       ngnt  auricle. 

It  is  only  in  a  heart  which  has  been  specially  injected  that  all  these  veins 
can  be  seen.  The  general  arrangement,  however,  can  usually  be  studied 
in  the  course  of  an  ordinary  dissection.  In  certain  cases,  where  the  veins 
are  empty  and  the  fat  on  the  surface  of  the  heart  scanty,  they  may  be 
inflated  with  air  by  introducing  a  blow -pipe  into  some  of  the  larger 
members  of  the  series. 

Cardiac  Nerves. — For  the  most  part  the  fine  nerves  which 
form  the  superficial  cardiac  plexus  are  prolonged  downwards 
upon  the  pulmonary  artery,  and  being  joined  by  a  considerable 
reinforcement  from  the  deep  cardiac  plexus,  they  form  the  right 
coronary  plexus  which  is  distributed  in  the  course  of  the  right 
coronary  artery.  The  left  coronary  plexus  which  accompanies 
the  artery  of  the  same  name  is  derived  from  the  deep  cardiac 
plexus.  The  nerves  do  not  slavishly  follow  the  arteries  ;  they 
soon  leave  the  vessels,  and  are  ultimately  lost  in  the  substance 
of  the  heart.  Here  and  there  ganglia  are  developed  in 
connection  with  them. 

Dissection.  — The  chambers  of  the  heart  should  now  be  opened  in  the 
order  in  which  the  blood  flows  through  them.  Begin  with  the  right  auricle, 
and,  to  bring  it  fully  into  view,  draw  the  heart  well  over  to  the  left  side  of 
the  body.  Two  cuts  are  required — (1)  A  vertical  incision  from  the  point 
at  which  the  superior  vena  cava  enters  the  auricle  to  the  point  of  entrance 
of  the  inferior  vena  cava.  In  making  this  incision,  care  must  be  taken  not 
to  injure  the  Eustachian  valve — a  fold  of  endocardium  placed  in  front  of 
the  mouth  of  the  inferior  vena  cava.  (2)  An  oblique  incision  carried  from 
about  the  middle  of  the  first  cut  to  the  tip  of  the  auricular  appendix.  The 
II — 4  a 


52 


THORAX 


Right  Auricle  (atrium  dextrum). 


Superior 
vena  cava 
Auricular 
appendix- 


dark  venous  blood  should  be  washed  away  from  the  interior  of  the  auricle 
with  a  sponge. 

When  the  dissector  has  fully  studied  the  interior  of  the  right  auricle, 
he  may  slit  open  with  the  scissors  the  superior  vena  cava  and  the  two 
innominate  veins.  By  this  proceeding  he  may  satisfy  himself  that  no  valves 
are  present  in  these  vessels. 

The  internal  surface  of 
the  cavity  presents  a 
polished  glossy  ap- 
pearance, due  to  its 
endocardial  lining.  In 
the  auricular  appendix 
the  wall  is  raised  into 
a  series  of  closely 
applied  parallel  mus- 
cular ridges,  called  the 
musculi  pectinati,  from 
their  resemblance  to 
the  teeth  of  a  comb. 
These  ridges  are  also 
present  on  the  right 
wall  of  the  auricle,  and 
when  followed  back- 
wards they  are  seen  to 
end  on  a  smooth  verti- 
cal ridge,  called  the 
crista  terminalis  (Figs. 
27  and  28).  It  re- 
presents in  the  interior 
of  the  auricle  the  groove 
on  the  exterior  already 
described  under  the 
name  of  the  sulcus 
terminalis.  In  the  in- 
tervals between  the 
musculi  pectinati  the 
wall  of  the  auricle  is 
very  thin.  To  the  left 
of  the  crista  terminalis 
the  walls  of  the  auricle  are  smooth  from  the  absence  of 
musculi  pectinati,  and  it  is  into  this  part  that  the  veins  open. 
The  blood  enters  the  atrium  of  the  auricle  by  the  following 
openings: — (1)  the  opening  of  the  superior  vena  cava;  (2) 


Atrium 

Musculi 
pectinati 


Crista 
terminalis 


Cut 


lferior  vena 


Fig.  27. — A  portion   of  the  Right  Auricle  from 
same  specimen  as  that  depicted  in  Fig.  22. 

The  auricular  part  of  the  heart  has  been  divided 
in  the  line  of  the  two  caval  veins,  the  anterior 
wall  of  the  right  auricle  removed,  and  then  the 
specimen  turned  slightly  over  to  the  right  so  as 
to  give  a  view  of  the  interior  of  the  appendix, 
etc.      The  specimen  was  hardened  in  situ. 


THORACIC  CAVITY 


53 


the  opening  of  the  inferior  vena  cava ;  (3)  the  opening  of  the 
coronary  sinus;  (4)  the  orifices  of  three  or  four  anterior 
cardiac  veins  from  the  surface  of  the  right  ventricle ;  (5)  the 
foramina  Thebesii. 

The  blood  flows  out  of  the  cavity,  into  the  right  ventricle, 
through  the  large  auriculo-ventricular  opening. 


Vena  azygos 
^^pl     major 


Pericardium 


Right 
bronchus 


Superior  vena  cava 


Musculi  pectinati 
Crista  terminalis 


Diaphragm 


Atrium  of  right 
auricle 


Inferior  vena 
cava 

Hepatic  vein 


Fig.  28. — Sagittal  section  through  the  Right  Auricle  of  the  Heart  and 
the  Root  of  the  Right  Lung. 


The  orifice  of  the  superior  vena  cava  is  situated  at  the 
upper  and  back  part  of  the  auricle.  It  should  be  noted  that 
this  aperture  is  devoid  of  a  valve,  and  that  the  upper  end  of 
the  crista  terminalis  is  continuous  with  the  sharply  defined 
anterior  border  of  the  opening.  The  inferior  vena  cava 
opens  into  the  lower  part  of  the  cavity,  and  has  the  rudi- 
mentary Eustachian  valve  in  relation  to  its  orifice.     The  dis- 


54 


THORAX 


(Fig- 


22. 


penor  vena  cava 


dix 
of  superior 


sector  should  note  that  these  two  veins  are  so  directed  that 
the  currents  of  blood,  which  flow  from  them  into  the 
auricle,  shall  not  be  opposed  the  one  against  the  other. 

The  auriculo-ventricular  orifice  is  the  large,   oval  opening 
situated   in    the   anterior  wall   of  the  atrium   of  the  auricle 
44).      Through  this  aperture  three  fingers   can 

be  readily  passed 
in  to  the  ventricle. 
If  the  student  now 
looks  between  this 
opening  and  the  ori- 
fice of  the  inferior 
vena  cava,  he  will 
discover  the  mouth 
of  the  coronary  sinus, 
imperfectlyguarded 
by  a  fold  of  endo- 
cardium, which  re- 
ceives the  name  of 
the  coronary  valve 
or  valve  of  Thebesius. 
An  attentive  ex- 
amination of  the 
inner  surface  of  the 
auricular  wall  will 
further  reveal 
several  minute, 
round,  irregularly 
scattered  openings 
called  the  j vram 1  n \a 

Fig.  29.— Interior  of  Right  Auricle  as  seen  by  the         . ,  ..        onrnp  nf 

removal  of  the  anterior  wall,  or  that  wall  op-  J- muesli,       ounic  ui 

posed    to    the    base    of   the    Ventricles.      This  these      are      simply 

is  a  part  of  the  same  specimen  that  is  depicted  small  ca^cal    pits  in 

in  Fig-  22"  the    substance     of 

the  heart,  whilst  others  are  the  mouths  of  minute  veins — 
the  venaz  Thebesii. 

Examine,  in  the  next  place,  the  partition  which  separates 
the  two  auricles  from  each  other  {septum  atriorum).  Upon 
this  an  oval  depression,  surrounded  by  a  prominent  ridge, 
will  be  noticed  a  short  distance  above  the  mouth  of  the 
inferior  vena  cava.  The  depression  is  called  the  fossa  ovalis. 
Its  floor  is  exceedingly  thin,  and  it  marks  the  position  of  the 


Crista  terminalis 


Tubercle  of 
Lower 

Annulus  ovalis 


Fossa  ovalis 

Left  auriculo- 
ventricular  orifice 

Opening  of 
coronary  sinus 

Thebesian  valve 


^—Eustachian  valve 


Cut  edge  of 
auricular  wall 
vena  cava 


THORACIC  CAVITY  55 

foramen  ovale  of  the  foetal  heart.  The  ridge  which  encircles 
it  is  deficient  below.  It  is,  therefore,  crescentic  in  form, 
and  is  called  the  annulus  ova/is  (limbus  fossse  ovalis).  In 
a  few  cases,  a  communication  between  the  two  auricles  may 
be  found  by  slipping  a  probe  under  the  upper  and  best- 
marked  part  of  the  annulus.  Stretching  between  the  anterior 
horn  of  the  annulus  ovalis  and  the  anterior  margin  of  the 
mouth  of  the  inferior  vena  cava  is  a  crescentic  fold  of 
endocardium,  sometimes  cribriform  and  often  very  feebly 
marked,  called  the  Eustachian  valve.  The  interauricular 
septum  in  the  interval  between  the  fossa  ovalis  and  the 
mouth  of  the  superior  vena  cava  exhibits  a  slight  promi- 
nence.    This  is  termed  the  tubercle  of  Lower. 

Dissection. — The  right  ventricle  may  now  be  opened  by  the  following 
incisions:— ( i)  An  incision  through  the  wall  of  the  ventricle  extending 
from  a  short  distance  below  the  auriculo  -  ventricular  groove  along  the 
sharp  margin  of  the  heart  to  the  lower  end  of  the  anterior  interventricular 
furrow.  (2)  A  transverse  incision,  through  the  anterior  wall  of  the 
ventricle,  from  the  upper  end  of  the  first  incision  to  the  upper  end  of  the 
anterior  interventricular  furrow.  This  cut  should  be  made  parallel  to  the 
auriculo-ventricular  groove,  and  about  half  an  inch  below  it.  Both  in- 
cisions must  be  made  with  care  and  deliberation,  but  more  especially  the 
second  one.  In  this  case  the  auriculo-ventricular  valve  is  liable  to  injury, 
and  it  is  well  to  protect  it  by  introducing  the  forefinger  of  the  left  hand 
through  the  auriculo-ventricular  opening  into  the  ventricle. 

The  anterior  wall  of  the  right  ventricle  can,  in  this  way,  be  raised  in 
the  form  of  a  V-shaped  flap  and  turned  to  the  left.  Wash  away  the  blood 
and  clots. 

Right  Ventricle  (ventriculus  dexter). — The  cavity  of  the 
right  ventricle,  now  laid  open  and  exposed  to  view,  is  of  a 
somewhat  triangular  form,  the  base  being  directed  backwards, 
and  the  apex  forwards  and  downwards  towards  the  apex  of 
the  heart.  It  does  not  reach  the  apex  of  the  heart,  however, 
but  corresponds  to  the  junction  of  the  anterior  and  inferior 
interventricular  furrows  around  the  sharp  margin  of  the  heart. 
On  transverse  section,  the  cavity  of  the  right  ventricle  is 
semilunar  in  outline,  owing  to  the  thick  fleshy  interventricular 
septum  which  constitutes  its  inner  wall  bulging  into  it  (Fig. 
30).  The  wall  is  thickest  at  its  upper  part,  and  thins 
slightly  towards  the  apex. 

With  the  exception  of  the  conus  arteriosus  or  infundi- 
bulum,  from  the  summit  of  which  the  pulmonary  artery 
arises,  and  the  interior  of  which  is  smooth  and  even,  the 
inner  surface  of  the  walls  of  the  right  ventricle  is  lendered 
extremely  irregular  by  the  projection  of  a  lace-work  of  fleshy 

II — 1  A 


56 


THORAX 


ridges  called  colu??ince.  carnece.  (trabecular  carneae).  It  is 
customary  to  describe  these  as  presenting  three  different 
forms — (a)  simple  elongated  ridges ;  (b)  fleshy  slips  or  trabe- 
cular free  throughout  the  greater  part  of  their  extent,  but 
fixed  to  the  wall  by  their  two  extremities ;  (c)  conical  fleshy 
projections  of  considerable  size,  which  project  into  the  cavity, 
and  are  attached  by  their  bases  only.  These  last  are  called 
musculi papillares,  and  are  arranged  so  as  to  form  an  anterior 
and  a  posterior  set.      The  free  end  of  each  of  these  papillary 

muscles  gives  origin  to 
several  delicate  thread-like 
tendon  s — the  chordaz  tendinece 
— and  by  these  they  are 
brought  into  connection  with 
the  segments  of  the  auriculo- 
ventricular  valve.  A  trans- 
verse fleshy  band  will  be 
noticed  to  spring  from  the 
base  of  the  anterior  papillary 
muscle,  and  stretch  across 
the  ventricular  cavity  to  the 
septum,  to  which  it  is  at- 
tached. This  is  the  moderator 
band.  By  fixing  the  yielding 
anterior  wall  of  the  ventricle 
to  the  more  solid  septum, 
it  is  said  to  prevent  over- 
distension of  the  cavity. 

There  are  two  openings 
in  the  right  ventricle — (i) 
the  aiiriculo-ventricular,  which 
gives  admission  to  the  stream 
of  blood;  (2)  the  pulmonary,  through  which  the  blood  passes 
into  the  pulmonary  artery.  Both  these  openings  are  situated 
at  the  base  of  the  ventricle.  The  large  oval  auriculo-ventri- 
cular  orifice  lies  to  the  right  and  behind,  whilst  the  pulmonary 
aperture  is  placed  to  the  left,  above  and  in  front  of  the  other, 
and  at  the  summit  of  the  conus  arteriosus.  Both  of  these 
openings  are  guarded  by  valves,  which  act  so  as  to  give  the 
blood  its  proper  direction  through  the  heart. 

The   valve   which    guards    the   mouth   of  the   pulmonary 
artery  is  composed  of  three  semilunar  segments,  and  is  called 


Fig.  30. — -Transverse  section  through 
the  Ventricular  Part  of  the  Heart. 
(From  Luschka. ) 

1.  Cavity  of  right  ventricle. 

2.  Cavity  of  left  ventricle. 

3.  Ventricular  septum. 

4.  Thick  wall  of  left  ventricle. 

5.  Thinner  wall  of  right  ventricle. 

6.  Inferior       interventricular       furrow 

with  middle  cardiac  vein  and  in- 
ferior hranch  of  right  coronary 
artery. 

7.  Anterior      interventricular     furrow, 

with  great  cardiac  vein  and  anterior 
branch  of  left  coronary  artery. 


THORACIC  CAVITY 


57 


the  semilunar  or  the  sigmoid  valve.  By  looking  upwards  into 
the  lumen  of  the  artery,  a  view  of  these  segments  may  be 
obtained,  but  it  is  better  to  defer  their  examination  until  the 
vessel  itself  has  been  studied. 

Right  Auriculo- Ventricular  or  Tricuspid   Valve  (valvula 
tricuspidalis). — This  valve  is   composed   of  three   triangular, 

Innominate  artery 
Left  subclavian  artery 
Left  common  carotid  artery 

Aortic  arch 

-  Serous  pericardium 

"Ascending  aorta 
Pulmonary  artery 

-Right  auricular  appendix 
Sinus  of  Valsalva 
Pulmonary  valve 


Superior  vena  cava 


Infundibulum 
Infundibular  segment 

Septal  segment 

Anterior  papillary 
muscle 
Moderator  band 


Inferior  vena  cava 


Marginal  segment 
FlG.  31. — The  Interior  of  the  Right  Ventricle. 


pointed,  membranous  segments,  termed  cusps,  which  project 
forwards  into  the  cavity.  These  are  united  by  their  bases  so 
as  to  form  an  annular  membrane,  and,  through  the  inter- 
mediation of  this,  they  are  fixed  around  the  auriculo-ventri- 
cular  opening.  In  the  intervals  between  these  larger  segments 
three  smaller  cusps  may  frequently  be  detected. 

Bach  cusp  is  composed  of  two  layers  of  endocardium, 
between  which  there  is  a  certain  amount  of  fibrous  tissue. 
This  fibrous  tissue  is,  for  the  most  part,  confined  to  the 
central  portion  of  the  cusp,  the  margins  of  which  are  there- 


53 


THORAX 


fore  thin  and  translucent.  When  the  valve  is  in  action,  it 
prevents  regurgitation  of  blood  into  the  auricle  during  the 
contraction  of  the  ventricular  wall.  Attached  to  the  ventri- 
cular surface  and  margin  of  each  segment,  as  well  as  into  the 
circumference  of  the  auriculo-ventricular  opening,  are  several 
of  the  chordae  tendineae  which  have  been  seen  to  take  origin 
from  the  apices  of  the  papillary  muscles.  In  consequence  of 
this,  the  ventricular  surface  of  the  valve  is  rough,  whilst  the 


eptal  musculi  papillares 

nfundibular  cusp 
-Septal  cusp 


Marginal  cusp 


Anterior  papillary 
muscle 


Posterior  papillary  muscle 


Fig.  32. — Diagram  of  the  arrangement  of  the  Cusps  and  Chordae  Tendineae 
of  the  Tricuspid  Valve. 

auricular  surface — that  surface  over  which  the  blood  flows — 
is  smooth. 

It  is  necessary,  however,  to  note  the  relative  position  of 
these  cusps.  One,  the  largest  of  the  three,  is  suspended  so 
as  to  intervene  between  the  auriculo-ventricular  opening  and 
the  pulmonary  orifice.  It  lies  in  front  and  to  the  left  of  the 
opening.  This  is  the  infundibular  cusp.  Another  is  placed 
posteriorly  to  the  auriculo-ventricular  opening,  and  lies  closely 
applied  to  the  septum.  This  is  the  septal  cusp.  The  third  is 
situated  to  the  right,  near  the  anterior  sharp  margin  of  the 
heart,  and  may  be  termed  the  marginal  cusp.  The  chordae 
tendineae  of  the  anterior  papillary  muscle  are  distributed  in  the 
interval  between  the  infundibular  and  marginal  flaps ;  those 
from  the  posterior  papillary  muscle  go  to  the  interval  between 


THORACIC  CAVITY 


59 


Pulmonary 

artery 


the  marginal  and  septal  flaps ;  whilst  to  the  interval  between 
the  infundibular  and  septal  flaps  pass  a  number  of  short  chordae 
tendineas,  some  of  which  spring  directly  from  the  septum, 
whilst  others  proceed  from  low,  feeble  musculi  papillares, 
also  connected  with  the  upper  part  of  the  septum. 

Pulmonary  Artery  (arteria  pulmonalis). — This  vessel  is  a 
short  wide  trunk  about  two  inches  long.  It  has  an  oblique 
direction  upwards  and  backwards,  so  as  to  reach  the  lower 
aspect  of  the  aortic  arch.  It  here  divides  into  a  right  and 
a  left  branch.  At  first,  it  lies  in  front  of  the  root  of  the 
aorta,  but,  as  it  ascends,  it  takes  a  spiral  turn  round  the 
ascending  aorta,  so  that  before  it  terminates  it  is  placed 
upon  the  left  side  of  that  vessel 
(Fig.  21,  p.  43).  In  relation 
to  each  side  of  the  pulmonary 
artery  the  dissector  will  notice 
the  corresponding  coronary 
artery  and  auricular  appendix. 
The  vessel  is  completely  en- 
closed within  the  fibrous  peri- 
cardium, the  serous  layer  of 
which  forms  a  single  tubular 
sheath  around  it  and  the  as- 
cending aorta. 

The  right  pulmonary  artery 
is  somewhat  longer  and  larger 
than  the  left.  It  passes  trans- 
versely outwards  behind  the  ascending  aorta  and  superior 
vena  cava  to  reach  the  root  of  the  right  lung,  where  it  has 
already  been  dissected  (Fig.  24,  p.  46).  The  left  pulmonary 
artery  runs  outwards  in  front  of  the  descending  aorta  and 
left  bronchus  to  gain  the  root  of  the  left  lung  (Fig.  39, 
p.  69).  The  blood  is  thus  conducted  from  the  right  ventricle 
of  the  heart  to  the  two  lungs. 

Ligamentum  Arteriosum  or  Obliterated  Ductus  Arteri- 
osus.— This  is  a  strong  fibrous  cord  which  will  be  observed 
connecting  the  upper  surface  of  the  root  of  the  left  pulmonary 
artery  with  the  under  surface  of  the  aortic  arch.  The  liga- 
mentum arteriosum  has  the  same  direction  as  the  trunk  of 
the  pulmonary  artery.  During  foetal  life  it  is  the  patent 
continuation  of  the  pulmonary  artery,  and  conducts  the  blood 
into  the  aorta.      At  this  period,  the  right  and  left  pulmonary 


Fig.  33.  — Heart  of  a  seven  months 
Foetus.      ( From  Gegenbaur. ) 


60  THORAX 

arteries  are  of  a  small  size,  and  convey  a  very  small  part  of 
the  blood-stream  to  the  lungs.  In  dissecting  the  fibrous 
remains  of  the  ductus  arteriosus,  note  that  the  left  recurrent 
laryngeal  branch  of  the  pneumogastric  nerve  hooks  round  it 
at  its  attachment  to  the  aorta. 

Dissection. — The  pulmonary  artery  may  now  be  slit  open,  so  as  to 
expose  the  valve  which  guards  its  orifice.  This  incision  must  be  made 
carefully,  and  the  knife  carried  upwards  through  the  wall  of  the  vessel  in 
the  interval  between  two  of  the  three  segments  which  enter  into  its 
formation. 

Pulmonary  Valve.  —  Each  semilunar  segment  will  be  ob- 
served to  be  attached  by  its  convex  margin,  whilst  its  concave 
border  is  free.  Three  minute  pouches  are  thus  formed 
around  the  mouth  of  the  vessel,  and  the  openings  of  these 
pouches  are  directed  upwards.  A  good  idea  of  the  valve  may 
be  obtained  by  filling  the  pouches  with  cotton  wadding.  The 
segments  consist  of  a  double  layer  of  endocardium,  strengthened 
by  intermediate  fibrous  tissue ;  and  if  the  free  margin  of  one 
be  taken  between  the  finger  and  thumb,  a  minute  nodule  of 
cartilage  may  be  felt  about  its  middle.  This  is  the  corpus 
Arantii.  In  structure,  these  little  flaps  are  similar  to  the 
corresponding  segments  of  the  aortic  valve — only  weaker. 
We  shall  defer  their  more  particular  description,  therefore, 
until  the  aortic  valve  is  under  consideration.  Opposite  each 
segment,  the  wall  of  the  artery  shows  a  slight  dilatation  or 
bulging,  called  the  sinus  of  Valsalva.  The  three  segments  of 
the  pulmonary  valve  are  so  placed  that  two  are  in  front  and 
one  behind  the  opening  (Fig.  31). 

Pulmonary  Veins  (venae  pulmonales). — The  blood  is  con- 
veyed back  to  the  heart  by  the  pulmonary  veins.  These 
have  already  been  studied  in  the  roots  of  the  lungs.  Two 
issue  from  each  lung.  The  right  veins  are  longer  than  the 
left,  and  pass  inwards  behind  the  superior  vena  cava  and  the 
right  auricle.  The  left  veins  pass  in  front  of  the  descending 
aorta  (Fig.  39).  If  the  inferior  vena  cava  be  now  divided 
and  the  heart  turned  upwards,  the  pulmonary  veins  will  be 
seen  opening  into  the  left  auricle  upon  its  posterior  aspect. 

Dissection. — To  open  the  left  auricle,  the  heart  must  be  turned  well 
over  to  the  right  side  of  the  body,  and  its  apex  tilted  forwards.  Enter  the 
knife  well  back,  and  carry  it  obliquely  forwards  into  the  auricular  appendix. 
The  cavity  is  usually  more  or  less  distended  with  injection,  and  after  this 
has  been  removed  the  walls  should  be  washed  with  warm  water. 


THORACIC  CAVITY 


61 


Left  Auricle  (atrium  sinistrum). — The  only  part  of  the 
left  auricle  which  can  be  seen  from  the  front  is  its  appendix. 
This  is  narrower  and  more  elongated  than  the  corresponding 
portion  of  the  right  auricle.  Its  margin  also  is  more  distinctly 
notched.  When  laid  open  it  will  be  seen  that  the  miisculi 
pecti?iati  are  confined  entirely  to  the  appendix.  Everywhere 
else  the  inner  surface  of  the  wall  of  the  left  auricle  is  smooth. 
On  the  posterior  wall  the  four  openings  of  the  pulmonary  veins 


A.  Aorta. 
P.  A.  The  right  and  left  pul- 
monary arteries. 
P.V.  Right  and  left  pulmon- 
ary veins. 
L.A.A.   Left  auricular  appendix. 
M.V.    Mitral  orifice. 
L.V.   Left  ventricle. 
R.V.   Right  ventricle. 
R.A.   Right  auricle. 
L.A.  Left  auricle. 
S.V.C.  Superior  vena  cava. 


Fig.  34. — Dissection  of  a  Heart  hardened  in  situ  to  show  the  Left  Auricle 
and  the  Left  Ventricle.  The  ascending  aorta,  the  anterior  cusp  of 
the  mitral  valve,  the  trunk  of  the  pulmonary  artery,  and  the  inter- 
auricular  septum  and  portion  of  the  interventricular  septum  have 
been  removed.      (Stiles.) 

will  be  seen.  In  some  cases  the  two  pulmonary  veins  of  one 
or  both  sides  unite  before  opening  into  the  left  auricle.  The 
number  of  venous  orifices  is  thus  reduced.  They  are  not 
provided  with  valves.  When  the  interior  of  the  left  auricle 
of  a  formalin-hardened  heart  is  examined  from  the  front  a 
projecting  crescentic  ridge  is  observed  to  pass  downwards  on 
the  left  wall  in  front  of  the  orifices  of  the  two  left  pulmonary 
veins  so  as  to  hide  them  from  view. 

In  the  fore-part  of  the  auricle  is  the  oval  auriculo-ventricular 
opening.      It  only  admits  the  passage  of  two  fingers  into  the 


62 


THORAX 


ventricle,  and  is  therefore  smaller  than  the  corresponding 
orifice  of  the  right  side.  The  position  of  the  fcetal  foramen 
ovale  can  also  be  distinguished  upon  this  side  of  the  septum 
atriorum,  but  it  is  not  so  well  marked  as  it  is  in  the  right 
auricle.  It  presents  the  appearance  of  a  faint  depression 
bounded  below  by  a  slightly  marked  crescentic  border. 
Foramina  Thebesii  and  the  small  orifices  of  venae  minimi 
cordis  are  also  present  on  the  walls  of  the  left  auricle. 

Dissection. — To  open  the  left  ventricle,  the  dissector  should  stand  upon 
the  right  side  of  the  body  and  grasp  the  heart  with  the  left  hand,  so  that 
the  forefinger  rests  upon  the  upper  part  of  the  inferior  interventricular 
furrow,  and  the  thumb  upon  the  upper  part  of  the  anterior  interventricular 
furrow.     The  wall  of  the  ventricle  should  then  be  transfixed  by  a  long 


Right  ventricle 


Left  ventricle — \ 


Septum 
ventriculorum 


Fig.  35. — Section  through  the  Ventricular  Portion  of  the  Heart  near  the 
apex.      It  shows  the  greater  depth  of  the  left  ventricle. 

knife.  Enter  the  knife  below  the  thumb,  about  half  an  inch  to  the  left  of 
the  anterior  furrow,  and  push  it  through  the  ventricular  wall  towards  the 
forefinger,  so  that  the  point  emerges  below  this,  and  half  an  inch  to  the 
left  of  the  inferior  furrow.  Now  carry  the  knife  downwards  towards  the 
apex,  but  do  not  allow  it  to  come  nearer  to  the  furrows  than  it  was  when 
first  entered.  If  necessary,  the  cut  on  each  side  may  be  extended  upwards 
towards  the  base  of  the  ventricle  with  a  small  knife. 

Left  Ventricle  (ventriculus  sinister). — The  cavity  of  the 
left  ventricle  is  longer  and  narrower  than  that  of  the  right 
ventricle.  It  reaches  down  to  the  apex  of  the  heart,  and  is 
somewhat  conical  in  shape — tapering  towards  its  lower  end. 
In  cross  section  it  presents  a  circular  or  broadly  oval  outline 
(Fig.  35).  The  walls  of  the  left  ventricle  are  very  much 
thicker  than  those  of  the  right  ventricle. 

When  the  injection  and  blood  have  been  washed  away 
from    the  interior  of  the   left   ventricle  with   hot   water,  the 


THORACIC  CAVITY 


63 


columnce  carnece  will  be  observed  to  form  dense  muscular 
reticulations  on  the  inner  surface  of  its  walls.  This  network 
is  especially  complicated  at  the  apex  and  on  the  inferior  wall 
of  the  cavity.  The  surface  of  the  septum  and  the  upper  part 
of  the  anterior  wall  are,  comparatively  speaking,  smooth. 
The  muscitli  fiapillares,  with  their  attached  chordae  tendineae, 
are  collected  into  two  strongly  marked  groups.  They  are 
much  larger  than  the  papillary  muscles  of  the  right  ventricle, 
but  do  not  project  so  distinctly  into  the  cavity. 

The   left   ventricle   has   two    openings — (1)  the   auriculo- 
ventricular   opening,    through    which   the   blood   enters   from 


Aortic  or  anterior  cusp 
Posterior  cusp 


Anterior 
papillary 
muscle 


Posterior  papillary 
muscle 


Fig.  36. — Diagram  of  the  arrangement  of  the  Cusps  and  Chordae  Tendinea? 

of  the  Mitral  Valve. 


the  auricle;  (2)  the  aortic  orifice,  through  which  the  blood 
flows  into  the  aorta.  These  apertures  are  situated  close 
together  at  the  base  of  the  ventricle,  the  auriculo-ventricular 
opening  lying  behind  and  to  the  left,  whilst  the  aortic  orifice  is 
placed  in  front  and  to  the  right.  Both  openings  are  guarded 
by  valves — the  auriculo-ventricular  opening  by  the  mitral  or 
bicuspid  valve,  and  the  aortic  opening  by  the  aortic  valve. 

Mitral  Valve  (valvula  bicuspidalis). — The  mitral  valve 
prevents  regurgitation  of  the  blood  into  the  left  auricle  during 
the  contraction  or  systole  of  the  ventricles.  It  consists  of 
two  large  pointed  cusps  with  two  smaller  portions  intervening. 
These  are  similar  in  structure  to  the  cusps  of  the  tricuspid 
valve,  but    the  segments  are    larger  and   much   stronger  and 


64  THORAX 

thicker.  The  fibrous  tissue  between  the  two  layers  of 
endocardium  is  more  abundant,  but  it  is  arranged  in  pre- 
cisely the  same  manner.  The  chordae  tendineae  from  each 
papillary  muscle  proceed  to  one  of  the  two  intervals  between 
the  cusps,  and  are  attached  to  the  adjacent  margins  and  to 
the  ventricular  surfaces  of  the  two  cusps.  The  anterior  or  aortic 
cusp  is  the  larger  of  the  two,  and  lies  in  front  and  to  the  right 
of  the  auriculo-ventricular  opening,  being  so  placed  as  to  inter- 
vene between  the  latter  and  the  aortic  aperture.  The  posterior 
or  marginal  cusp  lies  behind  and  to  the  left  of  the  opening. 

Aortic  Opening. — The  part  of  the  ventricular  cavity 
immediately  below  the  orifice  of  the  aorta  has  been  termed 
the  aortic  vestibule.  Its  walls  are  not  muscular  but  fibrous, 
and  therefore  it  does  not  collapse  during  the  diastole  of  the 
ventricular  part  of  the  heart.  This  is  of  advantage  in  so  far 
that  it  affords  space  for  the  proper  action  of  the  aortic  valve. 

Looking  upwards  into  the  circular  mouth  of  the  aorta, 
the  aortic  valve  will  be  seen.  It  is  similar  in  all  respects  to 
the  pulmonary  valve,  only  its  segments  are  stronger  and 
thicker,  and  the  sinuses  of  Valsalva  at  the  root  of  the  aorta 
are  more  strongly  marked.  The  aortic  valve  will  be  studied 
more  fully  at  a  later  stage  of  the  dissection. 

Septum  Ventriculorum. — The  septum  between  the  two 
ventricles  is  a  thick  fleshy  partition, — the  anterior  and 
inferior  attachments  of  which  are  indicated  on  the  surface 
of  the  heart  by  the  anterior  and  inferior  interventricular 
furrows.  Now  that  both  surfaces  of  the  septum  are  exposed, 
it  will  be  seen  to  be  thickest  near  the  apex  of  the  heart,  and 
to  thin  slightly  in  an  upward  direction.  In  its  basal  and  fore 
part  a  small  portion  may  be  noted  which  is  completely 
destitute  of  muscular  tissue,  and  which  consists  merely  of  the 
two  layers  of  endocardium,  with  some  intervening  fibrous 
tissue.  This  portion  is  termed  the  pars  membranacea  septi, 
and  it  is  of  interest  from  the  fact  that  it  is  at  this  point  that 
congenital  deficiency  of  the  septum  is  most  liable  to  occur. 
The  pars  membranacea  septi  forms  a  portion  of  the  wall  of 
the  aortic  vestibule,  and  lies  immediately  below  the  con- 
tiguous ends  of  the  anterior  and  right  posterior  flaps  of  the 
aortic  valve. 

Action  of  the  Heart. — The  above  details  will  be  dry  and  meaningless 
unless  they  are  looked  at  in  connexion  with  the  action  of  the  heart  during 
life.     It  is  impossible  to  understand  the  construction  of  the  heart  unless  we 


THORACIC  CAVITY  65 

study  at  the  same  time  its  function.  During  life,  the  blood  is  driven 
through  and  from  the  heart  by  means  of  successive  rhythmical  contractions 
and  dilatations  of  its  walls.  But  the  entire  heart  does  not  contract  simul- 
taneously. First,  the  auricles  contract  together,  and  this  is  succeeded  by 
the  contraction  of  the  ventricles  ;  in  other  words,  the  auricular  contractions 
correspond  to  the  ventricular  dilatations,  and  vice  versa.  But,  again,  there 
is  a  period  immediately  preceding  the  auricular  contraction,  during  which 
the  entire  heart  is  at  rest,  and  this  is  called  the  period  of  cardiac  rest. 
These  three  conditions  of  the  walls  of  the  heart— viz. ,  (a)  the  cardiac  rest, 
(b)  the  auricular  contraction,  (c)  the  ventricular  contraction — follow  each 
other  consecutively  and  without  intermission,  the  one  after  the  other  ;  and 
they  are  collectively  termed  "a  cardiac  revolution."  Let  us  study  what 
is  going  on  inside  the  heart  during  each  of  these  three  stages. 

During  the  period  of  cardiac  rest  the  auricles  are  filling.  Blood  is 
flowing  into  the  right  auricle  through  the  openings  of  the  superior  vena 
cava,  inferior  vena  cava,  and  the  coronary  sinus  ;  and  into  the  left  auricle 
through  the  orifices  of  the  four  pulmonary  veins.  A  portion  of  this  blood 
trickles  through  the  auriculo-ventricular  openings  into  the  ventricles  ;  but 
the  blood  is  passing  into  the  auricles  in  greater  quantity  than  it  is  trickling 
into  the  ventricles,  and  the  result  is,  distension  of  the  auricles.  The 
second  stage  of  the  cardiac  revolution  now  takes  place — viz. ,  the  auriadar 
contraction.  The  auricles  contract  sharply  and  suddenly,  and  the  blood  is 
forced  through  the  auriculo-ventricular  orifices  into  the  ventricles.  But 
how  is  it  that  the  blood,  during  this  contraction,  does  not  regurgitate  into 
the  veins,  the  mouths  of  which  are  devoid  of  valves  ?  For  the  simple 
reason  that  the  contraction  begins  at  the  venous  orifices  and  auricular 
appendices,  and  travels  towards  the  auriculo-ventricular  openings.  The 
ventricles  are  now  full,  and  the  third  stage  of  the  cardiac  revolution  takes 
place — viz.,  the  ventrictdar  contraction.  The  ventricles  contract  more 
slowly,  and  more  deliberately  than  the  auricles,  and  the  blood  is  discharged 
into  the  pulmonary  artery  and  into  the  aorta.  Regurgitation  of  blood 
through  the  auriculo-ventricular  openings  into  the  auricles  is  prevented  by 
the  apposition  of  the  segments  of  the  tricuspid  and  bicuspid  valves  ;  and 
when  the  ventricular  contraction  ceases,  regurgitation  from  the  arteries 
into  the  ventricles  is  prevented  by  the  semilunar  valves  being  thrown 
across  the  arterial  orifices. 

The  segments  of  the  auriculo-ventricular  valves  are  retained  in  position, 
and  prevented  from  being  forced  upwards  into  the  auricle  during  the 
ventricular  contraction,  by  the  musculi  papillares  and  the  chorda?  tendinese. 
As  the  ventricular  wall  in  its  contraction  to  a  certain  extent  advances 
towards  the  auriculo-ventricular  opening,  the  musculi  papillares,  in  their 
contraction,  retreat  from  it,  and  keep  the  tendinous  cords  tense — never 
allowing  them  to  slacken.  When  the  contraction  of  the  ventricle  ceases, 
and  the  vis  a  tergo  is  removed  from  the  blood,  the  recoil  of  the  expanded 
elastic  wall  of  the  artery  exerts  a  pressure  upon  the  column  of  blood.  Its 
backward  flow  is  prevented  by  the  filling  of  the  pouches  of  the  semilunar 
valve. 

Topography  of  the  Heart. — The  outline  of  the  heart  may  be  delineated 
on  the  anterior  surface  of  the  chest  as  follows: — (1)  draw  a  curved  line 
convex  outwards  from  the  sternal  end  of  the  third  right  costal  cartilage  to 
the  sternal  end  of  the  sixth  right  costal  cartilage  ;  this  line  should  attain 
its  point  of  maximum  convexity  as  it  crosses  the  fourth  intercostal  space, 
and  this  point  should  be  \\  inches  from  the  middle  line;  the  line  thus 
drawn  will  correspond  to  the  right  outline  of  the  right  auricle  ;  (2)  connect 
by  a  straight  line  the  sternal  end  of  the  sixth  right  costal  cartilage  with 

VOL.  II — 5 


66 


THORAX 


the  point  on  the  chest  wall  which  corresponds  to  the  apex  of  the  heart ;  this 
gives  the  lower  limit  of  the  heart,  and  for  the  most  part  it  corresponds  with 
the  margo  acutus  ;  (3)  from  the  apex  of  the  heart  draw  a  third  line  slightly 
curved  outwards  to  the  sternal  end  of  the  second  left  costal  cartilage  ;  this 
line  follows  on  the  surface  the  outline  of  the  margo  obtusus  and  the 
appendix  of  the  left  auricle. 


FlG.  37. — The  relations  of  the  Heart  and  of  its  Orifices  to  the  Anterior 
Thoracic  Wall.     (Young  and  Robinson. ) 


I  to  VII.  Costal  cartilages. 

A.   Aortic  orifice. 
Ao.  Aorta. 

C.  Clavicle. 
LA.   Left  auricle. 
LV.  Left  ventricle. 


M.   Mitral  orifice. 

P.  Pulmonary  orifice. 
RA.  Right  auricle. 
RV.   Right  ventricle. 
SVc.    Superior  vena  cava. 

T.  Triscuspid  orifice. 


An  oblique  line  extending  across  the  front  of  the  sternum  from  the 
middle  line  at  the  level  of  the  third  costal  cartilage  to  the  sternal  end  of 
the  sixth  right  costal  cartilage  indicates  on  the  surface  the  position  of  the 
auriculo -ventricular  groove. 

The  pulmonary  aperture  is  the  most  superficial  of  the  cardiac  orifices, 
and  lies  behind  the  upper  part  of  the  junction  of  the  third  left  costal 
cartilage  with  the  left  margin  of  the  sternum.  The  pulmonary  artery 
itself  lies  behind  the  anterior  end  of  the  second  left  intercostal  space  and 


THORACIC  CAVITY  67 

the  second  left  costo-sternal  articulation.  The  aortic  opening  is  placed 
more  deeply  and  at  a  slightly  lower  level.  It  is  situated  behind  the  left 
margin  of  the  sternum  opposite  the  lower  border  of  the  junction  between 
the  third  left  costal  cartilage  and  the  sternum.  The  right  aurictdo- 
ventricular  orifice  lies  behind  the  sternum,  opposite  the  extremity  of  the 
fourth  intercostal  space  of  the  right  side.  The  left  auriculo-ventriadar 
opening  is  very  deeply  placed.  It  is  situated  behind  the  left  margin  of  the 
sternum  at  the  level  of  its  junction  with  the  fourth  left  costal  cartilage. 

Dissection. — The   aorta   should    now   be    examined,    and    the   various 
structures  in  relation  to  it  must  be  carefully  dissected  out. 

Aorta. — The  aorta  is  the  great  arterial  trunk  which  con- 
veys blood  from  the  left  ventricle  of  the  heart,  and  distributes 
it  by  means  of  its  branches  to  every  part  of  the  body.  After 
leaving  the  heart  it  arches  over  the  root  of  the  left  lung,  and 
proceeds  downwards  in  front  of  the  vertebral  column.  It 
leaves  the  thoracic  cavity  by  passing  through  a  special  open- 
ing in  the  diaphragm,  and  it  ends  in  the  abdominal  cavity 
upon  the  left  side  of  the  body  of  the  fourth  lumbar  vertebra, 
by  dividing  into  the  two  common  iliac  arteries.  The  part 
of  this  great  vessel  which  is  contained  within  the  chest  is 
divided,  for  convenience  in  description,  into  three  portions : 
viz.,  the  ascending  aorta,  the  arch  of  the  aorta,  and  the  descending 
thoracic  aorta. 

The  ascending  aorta  takes  origin  from  the  base  of  the  left 
ventricle  of  the  heart,  and  proceeds  obliquely  upwards  and 
to  the  right  behind  the  sternum.  It  also  inclines,  to  some 
extent,  forwards,  so  as  to  approach  more  closely  to  the 
anterior  wall  of  the  chest.  Reaching  the  level  of  the  upper 
border  of  the  second  costal  cartilage  of  the  right  side,  it  changes 
its  direction,  and  passes  into  the  aortic  arch.  In  the  first 
instance  the  aortic  arch  bends  upwards  and  to  the  left  in 
front  of  the  trachea,  and  then  turns  suddenly  backwards  so 
as  to  gain  the  left  side  of  the  lower  border  of  the  body  of  the 
fourth  dorsal  vertebra.  Here  the  vessel  makes  a  bend  in 
a  downward  direction,  and  becomes  continuous  with  the 
descending  thoracic  aorta. 

Ascending  Aorta  (aorta  ascendens). — The  ascending  aorta 
takes  origin  from  the  base  of  the  left  ventricle  behind  the 
left  margin  of  the  sternum  opposite  the  lower  border  of  the 
third  costal  cartilage.  From  this  it  passes  upwards,  and  to 
the  right,  and  ends  in  the  aortic  arch  behind  the  right  margin 
of  the  sternum  at  the  level  of  the  upper  border  of  the  second 
costal  cartilage.  Throughout  its  entire  length  it  is  enclosed 
within   the   fibrous    pericardium,    whilst   the   same  sheath  of 


68 


THORAX 


serous  pericardium    surrounds  it  and  the  pulmonary  artery. 
It  is  therefore  placed  within  the  middle  mediastinum  (Figs. 

31  and  39,  PP-  57  and  69). 

It   does   not   possess    a    uniform    diameter.      At    its    root, 
opposite   the   segments   of  the   aortic   valve,    it  presents  the 


Internal 
g^  mammary 

,v -nyi;,-.: ;;-;..•.•.";.'  /      ^2^=^^,    ^  vessels 


Superior  vena 
cava 


Phrenic  nerve 
Aortic  arch 


Vagus  nerve-g 

Recurrent 

laryngeal  nerve 

Left  superior 

intercostal  vein 


GEsophagus-^S| 
Thoracic  duct-^HK. 

Sympathetic-* 


Phrenic  nerve 


Mediastinal 
pleura 

Trachea 

Vagus  nerve 

Intercostal 
"VB  arteries 
f^j  Vena  azygos 
BR  major 


^-* .|  Sympathetic 


Fig.  38. — Transverse  section  through  the  Superior  Mediastinum 
at  the  level  of  the  fourth  dorsal  vertebra. 

three  bulgings  termed  the  sinuses  of  Valsalva ;  whilst  higher 
up,  on  cross  section,  it  generally  exhibits  a  transversely  oval 
and  not  a  circular  outline.  This  is  due  to  the  presence  of 
a  diffuse  bulging  of  the  right  wall,  which  receives  the  name 
of  the  great  aortic  sinus.  Against  the  wall  of  this  sinus  the 
blood  is  driven  with  great  force  as  it  leaves  the  ventricle,  and 


THORACIC  CAVITY 


69 


at  first  sight  it  might  seem  to  be  aneurismal  in  its  origin, 
but  its  presence  in  the  foetus  renders  such  a  view  untenable. 
It  is,  however,  a  favourite  site  for  aneurismal  dilatation. 

The  more  immediate  relations  of  the  ascending  aorta  may 
now  be  examined.  It  is  intimately  associated  with  the 
pulmonary  artery  throughout  its  entire  length.      At  its  origin 


Left  phrenic 
nerve 

Pulmonary 
artery 

Left 

pulmonary 

artery 

( K>ophagus 

Left 
vagus  nerve 

Thoracic  duct- 
Descending 
aorta 

Vena  azygos 
minor  superior 


Internal 
-nammary 
vessels 


Pericardium 


Ascending  aorta 

Right  phrenic 
nerve 

Superior 
vena  cava 


Right  pulmon- 
ary artery 

Bifurcation  of 
trachea 
Right  vagus 
nerve 
Bronchial  artery 

Vena  azygos 
major 
Intercostal 
artery 

Sym  pathetic 

cord 


PlG.  39. — Transverse  section  through  the  Mediastinal  Space  at  the 
level  of  the  fifth  dorsal  vertebra. 

it  lies  behind  the  root  of  the  pulmonary  artery;  higher  up, 
this  vessel  is  placed  to  the  left  of  the  ascending  aorta.  To 
its  right  side,  and  partly  behind  it,  is  the  superior  vena  cava  ; 
whilst  behind,  it  is  in  relation  to  the  anterior  wall  of  the  right 
auricle  and  the  right  pulmonary  artery  (Fig.  24,  p.  46).  It 
is  overlapped  by  the  right  pleura  and  the  anterior  thin 
margin  of  the  right  lung,  which  intervene  between  it  and  the 
chest  wall. 


7o  THORAX 

The  coronary  arteries  have  already  been  seen  to  spring 
from  this  portion  of  the  aorta. 

Aortic  Arch  (arcus  aortae). — The  arch  of  the  aorta  extends 
from  the  termination  of  the  ascending  aorta  to  the  left 
side  of  the  body  of  the  fourth  dorsal  vertebra.  It  is  placed 
within  the  superior  mediastinum,  and  the  left  pleura  is 
applied  to  its  left  aspect  throughout  almost  its  entire  extent 
(Fig.  38).  It  lies  behind  the  manubrium  sterni,  and  as  it 
turns  backwards  it  is  crossed,  under  cover  of  the  left  media- 
stinal pleura,  by  the  left  phrenic  nerve,  the  inferior  cardiac 
branch  of  the  left  pneumogastric  nerve,  the  left  superior 
cardiac  branch  of  the  sympathetic,  and  the  left  pneumogastric 
nerve.  The  left  superior  intercostal  vein  ascends  upon  this 
surface  of  the  great  vessel  in  the  interval  between  the  vagus 
and  phrenic  nerves.  At  first  the  aortic  arch  lies  in  front  of 
the  trachea ;  afterwards  it  is  placed  to  the  left  of  the  trachea, 
the  oesophagus,  thoracic  duct,  and  the  left  recurrent  laryngeal 
nerve  (Fig.  38).  The  upper  border  of  this  subdivision  of  the 
aorta  is  in  relation  to  the  left  vena  innominata,  and  from  this 
aspect  of  the  vessel  three  large  arteries  take  origin,  viz.,  from 
right  to  left — (a)  the  innominate,  (p)  the  left  common  carotid, 
and  (c)  the  left  subclavian.  Its  lower  surface,  which  forms 
the  concavity  of  the  arch,  overhangs  the  bifurcation  of  the 
pulmonary  artery,  and  is  connected  with  the  root  of  the  left 
pulmonary  artery  by  the  fibrous  ligamentum  arteriosum. 
Hooking  round  this  surface  is  the  recurrent  laryngeal  branch 
of  the  left  vagus  nerve. 

Dissection. — The  three  large  branches  which  spring  from  the  aortic  arch 
carry  blood  for  the  supply  of  the  two  upper  limbs  and  the  head  and  neck. 
They  should  now  be  dissected.  The  left  common  carotid  takes  origin  some- 
what nearer  the  innominate  artery  than  the  left  subclavian.  They  are  all 
contained  within  the  superior  mediastinum,  ar.d  Fig.  40,  p.  71,  which 
is  taken  from  a  tracing  of  a  transverse  section  through  the  upper  part  of 
this  space  a  short  distance  above  the  level  of  the  aortic  arch,  shows  their 
more  important  relations. 

Innominate  Artery  (arteria  anonyma). — The  innominate 
artery  is  the  largest  of  the  three  branches  which  spring  from 
the  aortic  arch.  It  passes  obliquely  upwards  and  to  the  right 
in  the  superior  mediastinum,  and,  gaining  the  posterior  aspect 
of  the  right  sterno- clavicular  articulation,  ends  behind  the 
upper  margin  of  the  clavicle,  by  dividing  into  the  right 
common  carotid  and  right  subclavian  arteries.  In 1  front  of  the 
vessel  are  the  remains  of  the  thymus  gland  and  the  manubrium 


THORACIC  CAVITY 


71 


sterni,  to  the  posterior  aspect  of  which  are  attached  the 
sterno-hyoid  and  sterno-thyroid  muscles.  Further,  the  artery 
is  crossed  superficially,  and  close  to  its  origin,  by  the  left  vena 
innominata.  Behind  is  the  trachea  ;  but  as  the  vessel  inclines 
to  the  right,  it  comes  to  lie,  at  a  higher  level,  upon  the  right 
side  of  the  windpipe.  To  the  right  side  of  the  artery,  in  its 
upper  part,  are  the  pleura,  the  right  innominate  vein,  the 
superior  vena  cava,  and  the  right  phrenic  nerve. 


Left  innomi- 
nate vein 

Innominate 

Phrenic  nerve 

Left  common 

carotid 

Vagus  nerve 

Left  subclavian 

Recurrent 

laryngeal  nerve 

Mediastinal 

pleura 

Thoracic  duct 


Cartilage  of 
first  rib 
Internal  mam- 
mary vessels 
^^      Right  innomi- 
nate vein 
Phrenic  nerve 

Trachea 

Vagus 

Oesophagus 

Mediastinal 
pleura 


-->*«^gr: 


Fig.  40. — Transverse  section  through  the  Superior  Mediastinum 
at  level  of  the  third  dorsal  vertebra. 


With  the  exception  of  the  two  trunks  into  which  it  divides, 
the  innominate  artery  gives  off  no  branches.  The  thyroidea 
ima,  an  occasional  artery,  may  be  seen  to  spring  from  it  in 
some  cases. 

Left  Common  Carotid  Artery  (arteria  carotis  communis 
sinistra). — This  artery  ascends  in  the  superior  mediastinum  to 
the  posterior  aspect  of  the  left  sterno-clavicular  articulation. 
At  this  point  it  leaves  the  thorax  and  enters  the  neck.  It 
lies  deeply  in  the  thorax,  at  a  greater  distance  from  the 
manubrium   sterni   than   the  innominate  artery.      In  fro?it  of 


72  THORAX 

the  left  common  carotid  artery  are  the  remains  of  the  thymus 
gland,  and  the  left  vena  innominata,  which  crosses  it. 
Behind,  it  is  in  relation,  in  the  first  instance,  to  the  trachea, 
and  higher  up  to  the  oesophagus  and  thoracic  duct.  To 
its  left  side  are  the  left  phrenic  and  vagus  nerves.  Further, 
it  is  supported  on  the  left  side  by  the  left  pleura  and  lung. 
It  gives  off  no  branches  within  the  thoracic  cavity. 

Left  Subclavian  Artery  (arteria  subclavia  sinistra). — This 
vessel  springs  from  the  aortic  arch,  near  its  termination,  and  lies 
very  deeply  in  the  superior  mediastinum.  It  takes  a  vertical 
course  upwards  towards  the  thoracic  inlet,  through  which  it 
passes  by  arching  outwards  over  the  cervical  pleura  and  apex 
of  the  left  lung  to  gain  the  upper  surface  of  the  first  rib.  In 
front  is  the  left  common  carotid  artery,  the  left  vena  innomi- 
nata, and  the  left  pneumogastric  nerve.  To  its  right  side  are 
the  trachea  and  the  left  recurrent  laryngeal  nerve,  and  higher 
up,  the  oesophagus  and  thoracic  duct.  Behind  and  to  its  left 
side  are  the  left  mediastinal  pleura  and  the  left  lung.  The 
artery  lies  in  a  groove  on  the  inner  aspect  of  the  apex  of  the 
left  lung,  and,  before  the  dissection  of  the  mediastinum,  if  the 
apex  of  the  lung  be  pulled  outwards,  the  injected  artery  will 
be  seen  to  bulge  into  the  pleural  cavity. 

Dissection. — The  deep  cardiac  plexus  should  now  be  dissected.  Divide 
the  aortic  arch  at  its  commencement  and  termination.  Two  ligatures 
should  be  placed  around  the  vessel  at  each  of  these  points  and  the  section 
made  between  them.  This  is  done  to  prevent  the  escape  of  the  injection 
with  which  the  artery  is  filled.  The  superior  vena  cava  may  also  be  severed 
immediately  below  the  point  where  it  is  joined  by  the  vena  azygos  major. 
By  cutting  the  fibrous  ductus  arteriosus  the  aortic  arch  can  be  drawn  aside 
so  as  to  expose  the  trachea  and  the  cardiac  nerves  in  relation  to  it. 

Cardiac  Plexus  (plexus  cardiacus). — There  are  three  large 
nerve  plexuses,  formed  in  front  of  the  vertebral  column,  in 
connexion  with  the  sympathetic  system.  One  of  these,  the 
cardiac  plexus,  is  situated  within  the  thorax ;  the  other  two, 
the  solar  and  the  hypogastric  with  its  pelvic  prolongations,  are 
placed  within  the  abdomen. 

The  cardiac  plexus  is  subdivided  into  a  superficial  and  a 
deep  portion,  but  these  are  in  direct  connexion  with  each 
other,  and  are  to  be  regarded  merely  as  different  parts  of  one 
plexus.  The  deep  cardiac  plexus  is  further  massed  in  two 
portions  —  a  right  and  a  left — which  are  united  across  the 
middle  line  by  many  communicating  filaments. 

The  superficial  cardiac  plexus  is  small  in   comparison  with 


THORACIC  CAVITY  73 

the  deep  plexus.  It  has  already  been  examined,  and  has 
been  observed  to  lie  in  the  concavity  of  the  aortic  arch  in 
front  of  the  bifurcation  of  the  pulmonary  artery.  The  deep 
cardiac  plexus  is  situated  behind  the  aortic  arch  upon  the 
lower  end  of  the  trachea.  It  is  therefore  placed  on  a  deeper 
plane  and  at  a  slightly  higher  level  than  the  superficial  plexus. 
The  branches  which  enter  the  different  parts  of  the  cardiac 
plexus  are  derived  from  the  cervical  portions  of  the  gangliated 
cords  of  the  sympathetic,  from  the  pneumogastric  nerves,  and 
from  the  recurrent  daryngeal  nerves. 

The  sympathetic  cardiac  branches  which  arise  in  the  neck  are 
three  in  number  on  each  side — one  from  each  cervical  ganglion 
— and  they  are  termed  respectively  the  tipper,  middle,  and 
lower  sympathetic  cardiac  branches.  The  upper  sympathetic 
cardiac  branch  of  the  left  side  has  already  been  traced  across 
the  aortic  arch  into  the  superficial  cardiac  plexus. 

The  middle  and  lower  branches  of  the  left  side  join  the 
left  portion  of  the  deep  cardiac  plexus  on  the  trachea.  The 
three  sympathetic  cardiac  branches  of  the  right  side  join  the 
right  portion  of  the  deep  plexus.  Within  the  thorax  they 
run  obliquely  downwards  and  inwards  behind  the  innominate 
artery  to  reach  their  destination  on  the  side  of  the  trachea. 

The  cardiac  branches  of  the  pneumogastric  nerves  are 
given  off  partly  in  the  neck,  and  partly  in  the  thorax.  The 
cervical  branches  are  two  in  number,  viz.,  superior  and  inferior. 
The  inferior  cervical  cardiac  branch  of  the  left  pneumogastric 
has  been  previously  traced  over  the  aortic  arch  into  the  super- 
ficial cardiac  plexus.  Both  branches  on  the  right  side  proceed 
downwards  behind  the  subclavian  artery,  and  then  along  the 
trachea  to  join  the  right  portion  of  the  deep  cardiac  plexus. 
The  upper  branch  of  the  left  side  joins  the  left  part  of  the 
deep  cardiac  plexus. 

Thoracic  cardiac  branches  are  only  given  off  from  the  trunk 
of  the  right  pneumogastric.  They  join  the  right  portion  of 
the  deep  plexus. 

The  recurrent  laryngeal  branches  of  the  pneumogastric 
nerves  also  supply  cardiac  twigs  to  the  deep  plexus.  On  the 
left  side,  where  the  recurrent  laryngeal  hooks  round  the  arch 
of  the  aorta,  these  branches  are  more  numerous,  and  replace 
the  thoracic  cardiac  branches  of  the  left  pneumogastric.  The 
following  table  shows  the  arrangement  of  the  cardiac  nerves 
with  reference  to  the  plexus  : — 


74  THORAX 


c         c  •  i         i-         i  pathetic  of  left  side 

Superficial  cardiac  plexus,     .  •  -         T  •     i 

\  V  rwiTf^r    ceruiM       rare 


(i.   Superior  cardiac    branch  of  sym- 

I2' 

left  pneumogastric. 


Lower  cervical  cardiac  branch  of 


Left   portion   of  the  deep  cardiac 
plexus, 


Right  portion  of  the  deep  cardiac 
plexus,  .... 


f  I.   Middle  and  lower  cardiac  branches 
of  the  sympathetic  of  left  side. 

Upper  cervical  cardiac  branch  of 
the  pneumogastric. 

Cardiac  branches  of  the  left  recur- 
rent laryngeal, 
'i.   Three   cardiac    branches   of  sym- 
pathetic of  right  side. 

Both  cervical  cardiac  branches  of 
the  right  pneumogastric. 

Thoracic  cardiac  branches  of  the 
right  pneumogastric. 

Cardiac  branches  of  the  right  re- 
current laryngeal. 

The  manner  in  which  the  different  offsets  from  the  cardiac 
plexus  are  distributed  has,  to  a  certain  extent,  been  examined. 
From  the  right  portion  of  the  deep  plexus  proceed — (i)  an 
offset  to  join  the  right  anterior  pulmonary  plexus;  (2)  an 
offset  for  the  supply  of  filaments  to  the  right  auricle  of  the 
heart ;  and  (3)  a  very  considerable  prolongation,  which  passes 
downwards  in  front  of  the  right  pulmonary  artery  to  join  the 
superficial  cardiac  plexus,  and  form  the  right  coronary  plexus 

(p-  51). 

From  the  left  portion  of  the  deep  cardiac  plexus  proceed 
— (1)  an  offset  to  the  left  auricle;  (2)  an  offset  to  the  left 
anterior  pulmonary  plexus;  whilst  (3)  the  greater  part  of  it  is 
prolonged  downwards  in  relation  to  the  left  pulmonary  artery 
to  form  the  left  coronary  plexus  (p.  51). 

Removal  of  the  Heart  from  the  Body. — To  do  this  it  is  only  necessary 
to  divide  the  pulmonary  artery  and  the  pulmonary  veins.  The  other 
vessels  have  already  been  severed.  The  ascending  aorta  which  is  attached 
to  the  heart  should  next  be  slit  open,  care  being  taken  to  carry  the  knife 
accurately  between  two  of  the  segments  of  the  valve  so  as  not  to  injure 
either. 

Aortic  Valve.  — This  valve  may  now  be  studied  and  com- 
pared with  the  pulmonary  valve  which  guards  the  mouth  of 
the  pulmonary  artery.  The  membranous  valve  segments  are 
three  in  number,  and  are  of  semilunar  form.  Attached 
around  the  opening  by  their  convex  margins,  their  free  con- 
cave edges  project  into  the  lumen  of  the  vessel.  Three  little 
pockets,  open  towards  the  interior  of  the  artery,  are  in  this 
manner  produced.  In  the  case  of  the  pulmonary  artery  the 
segments  are  arranged  so  that  two  are  in  front  and  one  at  the 


THORACIC  CAVITY  75 

back  of  the  orifice.  In  the  aorta,  however,  one  lies  at  the 
front  and  two  at  the  back  of  the  opening,  and  on  looking 
into  the  sinuses  of  Valsalva,  which  correspond  to  the  segments, 
the  orifices  of  the  coronary  arteries  will  be  seen  (Fig.  25,  p. 
47).  Note  that  they  are  placed,  as  a  rule,  opposite  the  free 
edges  of  the  corresponding  valve  segments,  and  further,  that 
the  right  artery  springs  from  the  anterior  sinus  of  Valsalva, 
and  the  left  artery  from  the  left  posterior  sinus  of  Valsalva. 
There  are  no  such  openings  to  be  seen  in  the  pulmonary 
artery. 

The  aortic  valve  segments  are  constructed  upon  a  stronger 
plan  than  the  pulmonary  segments,  although  in  both  the 
structure  is  the  same.  In  the  aortic  segments  the  fibrous 
tissue  which  intervenes  between  the  two  layers  of  endocardium 
is  more  abundant,  and  the  corpora  Arantii  more  apparent. 
The  fibrous  tissue  is  not  uniformly  distributed  throughout  the 
valve  segment,  as  may  be  seen  by  placing  one  of  them  on  the 
point  of  the  finger.  A  firm  cord  runs  along  the  free  edge, 
and  also  along  the  attached  border.  In  addition  to  this,  the 
fibrous  tissue  is  spread  out  in  the  segment  in  a  uniform  layer, 
except  in  two  localities  called  the  lunula.  These  are  semi- 
lunar in  outline  and  lie  next  the  free  margin — one  on  either 
side  of  the  corpus  Arantii.  These  lunula  are  thin  and  trans- 
parent, seeing  that  they  are  formed  of  little  more  than  the 
two  opposed  layers  of  endocardium.  When  the  valve  is  in 
action  and  opposing  the  return  of  blood  into  the  heart  during 
diastole  of  the  ventricles,  the  thin  lunular  portions  of  the  valve 
segments  are  closely  applied,  and  afford  mutual  support  to 
each  other.  The  full  brunt  of  the  blood-pressure  is  borne  by 
the  stronger  portions  of  the  valve  segments. 

Cardiac  Wall. — The  last  step  in  the  dissection  of  the 
heart  consists  in  the  examination  of  the  parts  which  enter 
into  the  formation  of  the  cardiac  wall.  On  the  outside,  the 
heart  is  clothed  by  epicardium  or  serous  pericardium,  and  on 
the  inside  its  cavities  are  lined  by  the  thin  smooth  endocardium 
which  is  continuous  through  the  orifices  with  the  lining 
membrane  of  the  veins  and  arteries,  and  takes  a  large  share 
in  the  construction  of  the  valve-flaps.  Between  the  epi- 
cardium and  the  endocardium  is  placed  the  muscular  tissue 
of  the  heart,  which  is  termed  the  myocardium.  The  muscular 
fibres  of  the  heart  are  disposed  in  several  layers,  in  each  of 
which  the  fibres  take  a  special  direction. 


76  THORAX 

But  in  an  ordinary  dissecting-room  heart  very  little  information  can  be 
obtained  as  to  the  arrangement  of  the  muscular  fibres.  The  continuity  of 
the  walls  is  destroyed  by  the  openings  which  have  been  made  to  obtain  a 
view  of  the  interior  of  the  different  chambers.  It  is  better,  therefore,  to 
obtain  a  fresh  sheep's  heart.  After  filling  it  with  a  thick  mixture  of  flour 
and  water,  it  should  be  boiled  for  a  quarter  of  an  hour.  The  boiling  has 
the  effect  of  expanding  the  paste,  while  at  the  same  time  it  dissolves  the 
connective  tissue,  and  hardens  the  muscular  fasciculi.  When  the  boiling 
is  completed,  the  heart  should  be  placed  in  cold  water,  and  the  dissection 
carried  out.  The  epicardium  and  the  muscular  fibres  should  be  torn  off 
without  using  the  cutting  edge  of  the  scalpel. 

The  fibres  of  the  auricles  are  difficult  to  dissect ;  but  in  the  ventricular 
portion  of  the  heart,  the  student  should  be  able  to  make  out — (i)  that  the 
different  layers  of  muscular  fasciculi  cross  each  other  obliquely,  and  are  for 
the  most  part  attached  to  the  fibrous  rings  which  encircle  the  auriculo- 
ventricular  openings  ;  (2)  that  the  superficial  fasciculi  are  common  to  both 
ventricles  ;  (3)  that  the  majority  of  the  fasciculi  of  the  left  ventricle  bend 
inwards  at  the  ventricular  septum  ;  and  (4)  that  a  remarkable  spiral  or 
whorled  arrangement  of  fibres  (vortex  cordis)  occurs  at  the  apex  of  the 
heart. 

Construction  of  the  Ventricular  Orifices. — The  heart  which 
is  obtained  in  the  dissecting-room,  however,  must  not  be  cast 
aside,  because  several  very  essential  and  important  points 
may  be  made  out  by  its  further  dissection.  In  the  first  place, 
it  is  easy  to  determine  the  relation  of  the  auricles  and 
ventricles.  By  separating  the  epicardium  from  the  base  of 
the  ventricles  and  the  adjacent  part  of  the  auricles,  and  re- 
moving the  fat  and  vessels  from  the  auriculo-ventricular  furrow, 
it  will  be  seen  that  the  muscular  tissue  which  enters  into  the 
formation  of  the  ventricular  walls  is  quite  distinct  from  that 
of  the  auricular  walls.  At  only  one  place  is  there  a  direct 
continuity  between  the  muscular  tissue  of  the  auricles  and 
that  of  the  ventricles.  This  connecting  bridge  is  a  small 
slip,  termed  the  auriculo-ventricular  bundle,  which  passes 
from  the  septum  between  the  auricles  to  the  septum  between 
the  ventricles.  It  therefore  cannot  be  seen  from  the  outside 
of  the  heart. 

To  expose  the  auriculo-ventricular  bundle  the  right  auricle  and  right 
ventricle  should  be  opened  from  the  front,  and  the  anterior  half  of  the 
right  auriculo-ventricular  ring  removed.  The  septal  cusp  of  the  valve 
having  been  detached,  a  little  dissection  immediately  below  the  pars 
membranacea  septi  will  bring  the  bundle  into  view  as  it  passes  from  the 
septum  of  the  auricles  on  to  the  septum  of  the  ventricles.  It  is  easily 
distinguished  on  account  of  its  pale  colour.  At  the  lower  border  of  the 
pars  membranacea  septi  it  divides  into  two  parts.  One  part  is  carried  down 
on  the  right  face  of  the  ventricular  septum  and  the  other  upon  its  left  face. 

The  bond  of  union   between    the  auricles   and  ventricles 


THORACIC  CAVITY 


77 


consists  of  two  fibrous  rings  which  surround  the  auriculo- 
ventricular  openings.  By  removing  the  auricles  with  a  pair 
of  scissors  these  can  be  more  fully  displayed.  It  is  to 
these  rings  that  the  triangular  auriculo -ventricular  valve 
cusps  are  attached,  and  it  is  from  them  that  they  derive  the 


Portion  of  bundle  which  goes 
to  the  left  face  of  the  inter- 
ventricular septum 
Auriculo-ven-  ;v 

tricular  bundle^  -" 

/ 
Right  auricle 


Aorta 


Right  or  y 

marginal  flap    I 


Portion  of  sep 
tal  flap  of  tri 
cuspid  valve 


Posterior  papillary    ^v*W 
muscle 


Pulmonary  artery 
Os  cordis 

_lnfundibulum 

Portion  of  auricula- 
ventricular  bundle 
w-which  is  related  to  the 
right  face  of  the  inter- 
ventricular septum 


Interventricular 
septum 

Moderator  band  on 
which  fibres  from  the 
~auriculo-ven  tricular 
bundle  are  spread- 
ins  out 


FlG.  41. — Dissection  of  the  Heart  of  a  Calf  by  Dr.  Waterston  to  show  the 
Auriculo-ventricular  Bundle.  This  band  is  regarded  as  the  pathway  by 
which  the  wave  of  auricular  contraction  passes  from  the  auricular  to  the 
ventricular  wall. 


fibrous  tissue  which  intervenes  between  the  two  layers  of 
endocardium  which  form  them.  Two  fibrous  rings  are 
also  placed  around  the  arterial  openings,  and  supply  the 
strengthening  fibrous  tissue  to  the  semilunar  valve  segments. 

When  the  auricles  are  removed  from  the  ventricles,  the 
relative  positions  of  the  orifices  at  the  base  of  the  ventricular 
portion  of  the  heart  can  be  studied  (Fig.  25,  p.  47).     The 


7 


THORAX 


auriculo- ventricular  openings  lie  side  by  side  below  and 
posteriorly.  The  aortic  opening  is  placed  in  front  and  between 
them,  whilst  the  pulmonary  orifice  is  situated  in  front  of  the 
aortic  opening.  A  wide  interval  intervenes  between  the 
apertures  of  the  right  ventricle :  the  aortic  and  left  auriculo- 
ventricular  orifices,  however,  lie  close  together,  and  their 
fibrous  rings  for  a  short  distance  are  confluent  with  each 
other.  In  the  triangular  interval,  .between  the  aortic  and 
two  auriculo -ventricular  openings,  there  is  a  mass  of  fibro- 
cartilage  which  stands  in  intimate  connexion  with  the  fibrous 
rings. 

Dissection. — To  expose  the  trachea  more  fully,  separate  the  right  and 
left  pulmonary  arteries  with  the  knife,  and  throw  each  outwards  towards 

the  lung  with  which  it  is  connected. 
The  aortic  arch  must  be  drawn  aside, 
and  some  bronchial  glands  which  oc- 
cupy the  angle  between  the  bronchi 
removed. 


Trachea. — The  thoracic  por- 
tion of  the  trachea,  or  wind- 
pipe, traverses  the  superior 
mediastinum.  It  is  a  wide 
tube,  which  is  kept  constantly 
patent  by  a  series  of  cartilaginous 
rings  which  are  embedded  in 
its  walls.  Posteriorly  these  rings 
are  deficient,  and  in  consequence 
the  tube  is  flattened  behind.  Its 
appearance  in  transverse  section 
may  be  seen  in  Fig.  38,  p.  68. 
It  begins  in  the  neck  opposite 
the  sixth  cervical  vertebra,  where  it  is  continuous  with  the 
larynx,  and  it  enters  the  chest  cavity  through  the  thoracic  inlet. 
Here  it  lies  in  the  superior  mediastinal  space,  and  ends  by 
dividing  into  the  two  bronchi  opposite  the  intervertebral  disc 
between  the  fourth  and  fifth  dorsal  vertebras.  A  short  dis- 
tance above  the  bifurcation  an  impression,  sometimes  strongly 
marked,  is  usually  seen  on  the  left  side  of  the  trachea. 
This  is  due  to  the  close  contact  of  the  aortic  arch  as  it 
passes  backwards  against  this  part  of  the  tube.  Except  at 
its  lower  end,  which  is  very  slightly  inclined  to  the  right, 
the  trachea  adheres  rigorously  to  the  mesial  plane. 

The  relations  of  the  thoracic  part  of  the  trachea  are  as 


Fig.  42.  — Diagram  of  the  Base 
of  the  Ventricular  Portion  of 
the  Heart. 

P.  Pulmonary  opening. 
A.   Aortic  opening. 
L.   Left  auriculo-ventricular  opening. 
R.    Right  auriculo-ventricular    open- 
ing. 


THORACIC  CAVITY 


79 


follows  : — In  front — (i)  the  manubrium  sterni,  to  the  posterior 
aspect  of  which  the  sterno-hyoid  and  sterno-thyroid  muscles 
are  attached;  (2)  the  remains  of  the  thymus  body;  (3)  the 
left  innominate  vein ;  (4)  the  aortic  arch  and  the  origins  of 
the  innominate  and  left 
common  carotid  arteries ; 
(5)  the  deep  cardiac 
plexus.  Behind,  it  rests 
upon  the  oesophagus, 
which  lies  somewhat  to 
the  left  side  of  the  mesial 
plane.  On  its  right  side 
are  the  pleura  and  the 
right  pneumogastric 
nerve,  and  at  a  higher 
level  the  innominate 
artery ;  and  on  its  left  side 
are  the  aortic  arch,  the 
left  recurrent  laryngeal 
nerve,  and  the  left  sub- 
clavian artery  (Figs.  38 
and  40). 

Bronchi.  —  The     two 
bronchi    proceed    down- 
wards and  outwards  from 
the    termination    of 
the    trachea  —  each 
towards    the    hilum 
of  the  corresponding 
lung.        Like    the 
trachea,      they     are 
kept       permanently 
patent   by  the  pres- 
ence of  cartilaginous 
rings  in  their  walls. 
These  rings  are  de- 
ficient posteriorly,  so 

that  each  bronchus  exhibits  a  flattened  posterior  surface 
similar  to  that  of  the  trachea.  The  two  bronchi  differ  from 
each  other  in  length,  width,  and  in  the  direction  which  they 
pursue,  as  well  as  in  the  relations  which  they  present. 

The  first  collateral   branch  arises  from  the  right  bronchus 


Thyroid  cartilage 


Cricothyroid 
membrane 

Cricoid  cartilage 

Part  of  trachea 
covered  by  isthmus 
of  thyroid  body 


Common  carotid 
artery 

Left  subclavian 
artery 

Aortic  arch 


Left  bronchus 
Left  pulmonary 
artery 
/ 

Hyparterial 
bronchus 


Fig.   13 


■  Gullet 

hparterial  bronchus 
Hyparterial  bronchus 


Right  pulmonary  artery 

The  Trachea  and  Bronchi.      The  dotted 
line  gives  the  outline  of  the  thyroid  body. 


8c  THORAX 

much  nearer  the  trachea  than  in  the  case  of  the  left 
bronchus.  Taking  the  origin  of  this  branch  as  indicating 
the  terminal  limit  of  each  of  these  tubes,  the  left  bronchus 
is  at  least  twice  as  long  as  the  right  bronchus.  On  the  other 
hand,  the  right  bronchus  is  wider  than  the  left,  and  this  is 
clearly  due  to  the  greater  size  of  the  right  lung.  In  so  far 
as  the  direction  which  they  pursue  is  concerned,  it  will  be 
noticed  that  the  right  bronchus  takes  a  more  vertical  course 
than  the  left  bronchus.  It  therefore  lies  more  in  a  line  with 
the  trachea,  and  it  is  owing  to  this,  as  well  as  its  greater 
width,  that  when  foreign  bodies  are  introduced  into  the 
trachea  there  is  a  greater  tendency  for  them  to  enter  the 
right  bronchus.  The  more  horizontal  course  of  the  left 
bronchus  is  due  to  the  marked  projection  of  the  heart  to  the 
left  side  of  the  mesial  plane. 

Arching  forwards  over  the  right  bro?ichus  is  the  vena  azygos 
major,  whilst  the  vena  cava  superior  passes  downwards  in 
front  of  it.  Arching  over  the  left  bronchus  is  the  aortic  arch, 
whilst  passing  down  behind  it  are  the  oesophagus  and  the 
descending  thoracic  aorta.  On  each  side,  as  the  pulmonary 
artery  passes  outwards,  it  crosses  in  front  of  the  correspond- 
ing bronchus :  on  the  right  side  it  is  placed  below  the  first 
collateral  branch  (eparterial  bronchus),  on  the  left  side  it  lies 
above  the  first  collateral  branch  (first  hyparterial  bronchus). 
On  the  posterior  aspect  of  each  bronchus  the  vagus  nerve 
breaks  up  into  the  posterior  pulmonary  plexus.  Occupying 
the  angular  interval  between  the  bronchi  there  is  a  cluster  of 
bronchial  lymphatic  glands,  and  a  chain  of  these  glands 
accompanies  each  tube  towards  the  lung. 

A  small  fleshy  slip  passing  from  the  posterior  aspect  of 
the  left  bronchus  to  the  oesophagus  is  frequently  present. 
It  is  called  the  brotuho-xsophageal  muscle. 

The  relations  of  the  bronchi  in  the  roots  of  the  lungs  have 
already  been  studied  (p.  32). 

Posterior  Mediastinum. — This  term  is  applied  to  that 
part  of  the  interpleural  space  which  lies  behind  the  peri- 
cardium. It  may  be  regarded  as  a  continuation  downwards 
of  the  posterior  part  of  the  superior  mediastinum,  and  many 
of  the  structures  in  the  one  are  prolonged  downwards  into 
the  other.  The  arbitrary  upper  limit  of  the  posterior 
mediastinum  is  the  lower  border  of  the  fourth  dorsal 
vertebra.       In    front,    it    is    bounded    by    the    pericardium, 


THORACIC  CAVITY 


81 


except  in  its  very  lowest  portion,  where  the  anterior  wall  is 
formed  by  the  posterior  surface  of  the  diaphragm  (Fig.  45). 
Behind,  it  is  limited  by  the  bodies  of  the  dorsal  vertebrae 
below  the  fourth,  and  on  each  side  by  the  mediastinal  pleura 
as  it  passes  back  from  the  pericardium  to  the  spine.  In 
transverse  section  its  outline  is  quadrilateral.  Figs.  44 
and  45  are  taken  from  tracings  of  transverse  sections 
through  the  space.  They  serve  to  show  the  character  of 
the  space  and  the  relative  positions  of  some  of  the  more 
important  contents.  The  following  is  a  list  of  the  structures 
which  it  contains  : — 


Pericardium 


Thoracic 


Vena  cava  inferior 


CEsophagus 

Thoracic  duct 
Vena  azygos  major 

Pleura 


Fig.  44.- 


-Tracing  of  section  through  the  Posterior  Mediastinum 
at  the  level  of  the  eighth  dorsal  vertebra. 


1.  The  descending  thoracic  aorta. 

2.  The  oesophagus. 

3.  The  pneumogastric  nerves. 

4.  The  thoracic  duct. 

5.  The  vena  azygos  major 


6.  Certain  of  the  right  aortic  inter- 

costal arteries. 

7.  The  vena  azygos  minor  superior. 

8.  The  vena  azygos  minor  inferior. 
The  great  splanchnic  nerves. 


10.   Some  lymphatic  glands. 

Dissection. — To  open  into  the  posterior  mediastinal  space  it  is  neces- 
sary to  make  a  vertical  incision  through  the  pericardium,  which  forms 
its  anterior  wall.  Carry  the  knife  along  the  line  of  the  oesophagus,  and 
throw  the  pericardium  outwards.  If  this  be  done  with  care,  a  fleshy 
band  may,  in  some  cases,  be  observed  crossing  the  superficial  aspect  of 
the  thoracic  aorta,  and  extending  from  the  oesophagus  to  the  pleura, 
which  forms  the  left  lateral  wall  of  the  posterior  mediastinal  space. 
This  is  the  plenro-cesophageal  mitscle.  In  the  majority  of  cases,  however, 
this  muscle  is  only  represented  by  a  few  slender  muscular  fasciculi,  which 
are  difficult  to  isolate  from  the  areolar  tissue  in  which  they  lie. 

Pneumogastric   Nerves  (nervi  vagi). — The  pneumogastric 
nerves  can   now  be  followed  throughout    their  entire  course 
vol.  11 — 6 


82  THORAX 

within  the  thorax.  They  traverse  both  the  superior  and 
posterior  mediastinal  spaces,  but  differ  so  much  in  their 
relations  on  the  two  sides  of  the  body  that  it  is  best  to 
examine  each  separately. 

The  left  pneumogastric  nerve  enters  the  thorax  in  the  in- 
terval between  the  left  common  carotid  and  left  subclavian 
arteries,  and  behind  the  left  innominate  vein  (Fig.  40,  p.  71). 
It  has  already  been  observed  crossing  the  arch  of  the  aorta 
behind  and  to  the  left  side  of  the  -phrenic  nerve  and  the  two 
superficial  cardiac  nerves  (Fig.  38,  p.  68).  Here  also  it  has 
been  seen  to  give  off  its  recurrent  laryngeal  branch.  Leaving 
the  aorta,  it  sinks  behind  the  root  of  the  left  lung  (Fig.  39, 


Pericardium 


Diaph 


Diaphragm 
CEsophagus 


Thoracic  aorta   f^4 
Left  pleura     pf| 

s 


...  Thoracic  duct 

QTifiV;""  Right  Pleura     . 

Vena  azygos  major 


Fig.  45. — Tracing  of  a  section  through  the  lower  part  of  the 
Posterior  Mediastinum,  where  its  anterior  wall  is  formed  by  the 
diaphragm. 


p.  69),  and  at  once  breaks  up  into  a  number  of  branches,  which 
unite  in  a  plexiform  manner  to  form  the  left  posterior  pulmon- 
ary plexus.  It  issues  from  this  plexus  in  the  form  of  one  or 
two  cords,  which  pass  to  the  anterior  aspect  of  the  oesophagus. 
Upon  the  oesophagus  another  plexus — the  plexus  gulce — is 
formed.  Both  of  the  pneumogastric  nerves  take  part  in  the 
formation  of  this  plexus.  From  the  plexus  gulae  the  left 
pneumogastric  emerges  as  one  trunk,  and  passes  out  of  the 
thorax  by  the  oesophageal  opening  of  the  diaphragm.  Within 
the  abdomen  it  breaks  up  into  branches  upon  the  anterior 
surface  of  the  stomach. 

The  right  pneumogastric  nerve,  in  the  upper  part  of  the 
superior  mediastinum,  lies  deeper  in  the  thorax  than  the 
left    nerve.       It  enters   by  passing    between  the    subclavian 


THORACIC  CAVITY 


83 


artery  and  the  right  innominate  vein,  and  descends  by  the  side 
of  the  trachea  (Figs.  40  and  38)  to  the  posterior  aspect  of  the 
root  of  the  right  lung  (Fig.  39,  p.  69).  Here  it  breaks  up  into 
the  right  posterior  pulmonary  plexus,  and,  issuing  from  this  in 
the   form  of  two  nerve   cords,  it  takes  part  in  the  formation 


Left  common  carotid  artery 
Left  vagus  nerve 


Left  subclavian  artery 
Left  innominate  vein 


Trachea 


Left  pulmonary 
artery' 

Left  bronchu 


Left  pulmonary 
veins 


Right  vagus  ner\ 


I  diaphragmatic 

surface  of  heart 


Innominate  artery 
(Esophagus 

Right  vagus  nerve 


Superior  vena  cava 


Vena  azygos  major 

Right  posterior 
pulmonary-  plexus 
5|    Right  pulmonary 
artery 


Right  bronchus 


Right  pulmonary- 
veins 

Plexus  gulae 


Portion  of  peri- 
cardium 


Left  vagus  nerve 
Inferior  vena  cava 


FlG.  46. — Posterior  Aspect  of  the  Heart  with  the  Descending  Aorta,  the 
Trachea  and  Bronchi,  and  the  CEsophagus. 

of  the  plexus  gulce.  It  leaves  this  plexus  upon  the  posterior 
aspect  of  the  oesophagus,  and,  entering  the  abdomen  through 
the  oesophageal  opening  of  the  diaphragm,  it  breaks  up  into 
branches  on  the  posterior  aspect  of  the  stomach. 

The  pneumogastric  nerves  give  off  the  following  branches 
within  the  thorax  : — 
11 — 6  a 


84  THORAX 

1.  Recurrent  laryngeal  (left  side). 

2.  Thoracic  cardiac  (right  side). 

3.  Pulmonary. 

4.  Oesophageal. 

5.  Pericardial. 

The  left  recurrent  laryngeal  nerve  (nervus  laryngeus  inferior 
sinister)  springs  from  the  pneumogastric  as  it  crosses  the  arch 
of  the  aorta.  It  hooks  round  the  aortic  arch,  or  rather  the 
attachment  of  the  ligamentum  arteriosum  to  the  under  surface 
of  the  arch,  and  reaching  the  trachea,  ascends  in  the  interval 
between  this  and  the  oesophagus  to  the  larynx.  The  right  re- 
current laryngeal  nerve  (nervus  laryngeus  inferior  dexter)  arises 
in  the  root  of  the  neck,  and  hooks  round  the  subclavian  artery. 

The  thoracic  cardiac  branches  (rami  cardiaci  inferiores)  ot 
the  right  side  proceed  in  part  from  the  pneumogastric  and 
in  part  from  the  recurrent  laryngeal  nerve  of  that  side.  On 
the  left  side  of  the  body  they  are  derived  from  the  left  re- 
current laryngeal  nerve  as  it  turns  round  the  aortic  arch. 

The  pulmonary  branches  have  already  been  studied  in 
connexion  with  the  root  of  the  lung  (pp.  31,  32). 

The  oesophageal  branches  (rami  cesophagei)  are  dispensed 
to  the  gullet  in  two  sets — (1)  a  few  delicate  twigs  are  given 
by  the  pneumogastric  before  it  enters  the  pulmonary  plexus 
to  that  portion  of  the  oesophagus  which  lies  in  the  superior 
mediastinum;  (2)  numerous  filaments  are  supplied  by  the 
plexus  gulae  to  that  part  of  the  oesophagus  which  is  placed 
in  the  posterior  mediastinum. 

The  pericardial  branches  are  a  few  fine  filaments  which 
come  from  the  plexus  gulae  and,  perhaps,  from  the  posterior 
pulmonary  plexus  and  enter  the  back  of  the  pericardium. 

(Esophagus. — The  thoracic  portion  of  the  oesophagus 
should  next  be  studied.  It  lies  partly  in  the  superior 
mediastinum  and  partly  in  the  posterior  mediastinum.  It  is 
the  narrowest,  but  at  the  same  time  the  most  muscular,  part 
of  the  alimentary  canal.  It  descends  in  front  of  the  spine, 
following  its  antero-posterior  curvature,  and  leaves  the  thoracic 
cavity  opposite  the  tenth  dorsal  vertebra  by  passing  through 
the  oesophageal  opening  of  the  diaphragm.  The  oesophagus 
does  not  pursue  a  straight  course  through  the  thorax :  it 
enters  somewhat  to  the  left  of  the  middle  line  ;  but  on  tracing 
it  downwards,  it  will  be  noticed  to  incline  inwards,  so  as  to 
assume  a  mesial  position  opposite  the  fifth  dorsal  vertebra. 


THORACIC  CAVITY  85 

From   this   it   again   deviates   to   the  left  so  as  to   gain   the 
oesophageal  opening  in  the  diaphragm. 

In  the  superior  mediastinum  the  oesophagus  lies  immedi- 
ately behind  the  trachea  (Figs.  40  and  38);  below  this,  it 
is  crossed  by  the  left  bronchus,  with  which  it  is  sometimes 
connected  by  the  broncho -oesophageal  muscle  (Fig.  39). 
From  this  point  onwards  through  the  posterior  mediastinum 
it  is  covered  in  front  by  the  pericardium,  which  is  applied 
closely  to  it  (Fig.  44).  Just  before  entering  the  abdomen 
it  lies  behind  the  posterior  part  of  the  diaphragm  (Fig.  45). 
From  above  downwards,  therefore,  the  immediate  anterior 
relations  of  the  oesophagus  are  :  (1)  trachea  ;  (2)  left  bronchus  ; 
(3)  pericardium ;  (4)  diaphragm.  Behind,  the  gullet  lies, 
except  at  its  lower  end,  in  front  of  the  vertebral  column,  but 
there  are  many  structures  which  intervene  between  them. 
Thus,  in  the  superior  mediastinum  the  longus  colli  muscle 
separates  the  gullet  from  the  spine,  while  in  the  posterior 
mediastinum  it  is  placed  in  front  of  the  vena  azygos  major 
and  the  thoracic  duct.  The  vena  azygos  minor  inferior  and 
superior  and  the  right  intercostal  arteries  also  cross  behind  it. 
In  its  lower  part,  the  gullet  inclines  forwards  and  to  the  left, 
so  that  it  comes  to  rest  directly  upon  the  anterior  surface  of 
the  thoracic  aorta.  These  relations  are  seen  in  Figs.  44  and  45. 
Upon  the  right  side,  during  its  course  through  the  posterior 
mediastinum,  the  oesophagus  is  clothed  by  the  mediastinal 
pleura,  whilst  on  the  left  side  it  is  related  in  the  posterior 
mediastinum  to  the  thoracic  aorta,  except  where  in  its  lower 
part  it  lies  in  front  of  that  vessel  (Fig.  45).  In  the  superior 
mediastinum  the  thoracic  duct  is  closely  applied  to  the  left 
side  of  the  oesophagus,  and  the  left  pleura  comes  into  relation- 
ship with  it  (Fig.  40,  p.  71).  Below  this,  however,  except 
immediately  above  the  point  where  it  pierces  the  diaphragm, 
it  is  not  directly  related  to  the  pleura  of  the  left  side. 

The  pneumogastric  nerves  form  the  plexus  guise  on  the 
walls  of  the  gullet,  as  it  traverses  the  posterior  mediastinum, 
and  accompany  it  in  the  form  of  two  nerve-trunks  through 
the  oesophageal  opening — the  right  nerve  being  placed  on  its 
posterior  aspect,  whilst  the  left  nerve  is  placed  in  front  of  it. 

Descending     Thoracic     Aorta     (aorta     thoracica).  —  The 

descending  thoracic  aorta  is  the  direct  continuation  of  the 

aortic  arch,  and  it  traverses  the  posterior  mediastinum.     It 

begins  at  the  lower  border  of  the  fourth  dorsal  vertebra,  and 

n— 6  6 


86  THORAX 

ends  opposite  the  last  dorsal  vertebra  by  entering  the  abdomen 
through  the  aortic  opening  of  the  diaphragm,  and  becoming 
the  abdominal  aorta.  At  its  commencement  it  lies  somewhat 
to  the  left  of  the  middle  line,  but  as  it  proceeds  downwards 
it  inclines  inwards,  so  that  at  its  termination  it  is  mesial  in 
position.  It  lies  upon  the  bodies  of  the  vertebrae,  and 
therefore  it  shows  a  curve  corresponding  to  that  of  the 
vertebral  column  in  the  dorsal  region.  In  fro?it,  it  is  crossed 
by  the  root  of  the  left  lung.  Below  this,  it  is  covered  by  the 
pericardium  and  the  posterior  part  of  the  diaphragm.  Behind, 
it  rests  upon  the  vertebral  bodies  and  the  intervening  inter- 
vertebral discs,  whilst  crossing  behind  it  the  dissector  will 
observe  the  vena  azygos  minor  inferior,  and,  in  many  cases, 
the  vena  azygos  minor  superior.  To  the  left  side,  and  closely 
applied  to  the  vessel,  is  that  part  of  the  pleura  which  forms 
the  left  lateral  wall  of  the  posterior  mediastinum ;  whilst  on 
its  right  side  will  be  noticed  the  thoracic  duct  and  the  vena 
azygos  major. 

The  oesophagus  presents  important  relationships  to  the 
thoracic  aorta.  At  first  it  lies  to  the  right  of  the  aorta,  but  as 
it  approaches  the  diaphragm  it  inclines  to  the  left,  and  comes 
to  lie  in  front  of  the  vessel ;  and  lastly,  before  it  passes  through 
the  oesophageal  opening  of  the  diaphragm,  it  is  somewhat  to 
its  left  side  and  still  distinctly  in  front. 

The  Branches  of  the  Descending  Thoracic  Aorta  may  be 
grouped  under  the  heads  of  visceral  and  parietal. 


Visceral. 


Bronchial. 

Pericardial. 

(^Esophageal. 


|( 

V.  Posterior  mediastinal. 

p     .      .         j  Intercostal  (nine  on  each  side). 
-L  arietai.       ~i  o  i_       *.  i 
{ Subcostal. 

The  bronchial  arteries  (arteriae  bronchiales)  are  usually 
three  in  number — two  for  the  left  lung  and  one  for  the  right 
lung.  They  are  very  variable  in  their  manner  of  origin. 
The  right  bronchial  artery  often  springs  from  the  first  right 
aortic  intercostal  artery.  The  left  bronchial  arteries  generally 
take  origin  from  the  aorta.  They  run  upon  the  posterior 
aspect  of  the  corresponding  bronchus,  and  they  have  already 
been  studied  as  constituent  parts  of  the  roots  of  the  lungs. 
In  the  substance  of  the  lung,  they  follow  the  bronchi,  and 
show  a  similar  mode  of  branching  and  distribution. 


THORACIC  CAVITY  87 

The  bronchial  veins  are  of  small  size.  The  left  opens  into 
the  vena  azygos  minor  superior;  the  right  joins  the  vena 
azygos  major. 

The.  pericardial  branches  (rami  pericardiaci)  are  some  minute 
twigs  which  are  distributed  to  the  posterior  aspect  of  the 
pericardium. 

The  oesophageal  arteries  (arteriae  oesophageal)  are  the  vessels 
of  supply  to  the  gullet.  They  are  four  or  five  in  number, 
and  are  irregularly  placed.  They  spring  from  the  front  or 
right  side  of  the  aorta,  and  form  a  chain  of  anastomosing 
branches  on  the  wall  of  the  oesophagus.  Above,  this  chain 
communicates  with  branches  of  the  inferior  thyroid  artery, 
whilst  below,  it  communicates  with  the  ascending  oesophageal 
branches  of  the  coronary  artery  of  the  stomach. 

The  posterior  jnediastinal  branches  (rami  mediastinales)  are 
very  small,  and  are  given  to  the  areolar  tissue  and  glands  in 
the  posterior  mediastinal  space. 

The  i?itercostal  branches  (arteriae  intercostales)  will  be 
observed  arising  in  pairs  from  the  posterior  aspect  of  the 
aorta.  Defer  their  examination  until  the  thoracic  duct  and 
the  sympathetic  cords  have  been  dissected.  The  pair  of 
subcostal  arteries  lie  in  series  with  the  intercostal  branches,  and 
may  be  studied  along  with  them. 

Thoracic  Duct  (ductus  thoracicus). — The  thoracic  duct, 
although  a  vessel  of  small  calibre,  is  one  of  high  importance. 
It  receives  all  the  lymphatic  vessels  of  the  body  below  the 
diaphragm  (except  those  from  part  of  the  upper  surface  of 
the  liver),  the  lymphatics  of  the  left  side  of  the  chest  (in- 
cluding the  left  lung  and  left  side  of  the  heart),  and  the 
lymphatics  of  the  left  superior  extremity  and  left  side  of  the 
head  and  neck.  It  will  be  found  by  dissecting  in  the  loose 
areolar  tissue  which  lies  between  the  aorta  and  the  vena 
azygos  major,  and  it  will  be  recognised  from  its  position,  and 
by  the  great  elasticity  which  it  exhibits  when  it  is  pulled  by 
the  forceps.  Trace  it  downwards,  and  it  will  be  found  to 
enter  the  thorax  upon  the  right  side  of  the  aorta,  and  through 
the  same  opening  in  the  diaphragm.  It  commences  within 
the  abdomen  upon  the  bodies  of  the  first  and  second  lumbar 
vertebrae  as  an  elongated  dilatation,  called  the  receptaculum 
chyli.  At  the  level  of  the  fifth  dorsal  vertebra  it  passes  from 
the  right  to  the  left  of  the  mesial  plane  by  crossing  behind 
the   oesophagus  (Fig.   39,   p.  69).     It  now  ascends  into  the 

11— 6  c 


88 


THORAX 


neck  between   the   oesophagus  and  left  pleura,   and   arching 


17 18 


Fig,  47. — The  Thoracic  Duct  and  \\s  Tributaries. 


1.  Lumbar  veins. 

2.  Left  renal  vein. 

3.  Right  renal  artery. 

4.  Inferior  vena  cava. 

5.  Suprarenal  body. 

6.  Receptaculum  chyli. 

7.  Thoracic  duct. 
S.  Descending  thoracic 

lymphatic  trunk. 
9.   Vena  azygos  major. 

0.  Mediastinal  lymphatic 
vessel. 

1.  Superior  intercostal  vein. 

2.  Subclavian  vein. 

3.  Subclavian  artery. 

4.  Clavicle. 

5.  Scalenus  anticus  muscle. 
Phrenic  nerve. 
Thyroid  axis. 
Internal  jugular  vein. 
Vertebral  artery. 

20.  Common  carotid  artery. 

21.  Trachea. 

22.  Thyroid  body. 

23.  (Esophagus. 

24.  Common  carotid  artery. 

25.  Internal  jugular  vein. 

26.  Vertebral  artery. 

27.  Thyroid  axis. 

28.  Common  lymphatic 
trunk  from  head  and 
upper  limb. 

29.  Scalenus  anticus  muscle. 

30.  Subclavian  artery. 

31.  Superior  intercostal  vein. 
Bronchial  lymphatic 

vessel. 
Vena  azygos  minor 

superior. 
Aorta. 
Vena  azygos  minor 

inferior. 

36.  (Esophagus. 

37.  Descending  thoracic 
lymphatic  trunk. 

Inferior  phrenic  artery. 
Suprarenal  body. 
Cceliac  axis. 
Superior  mesenteric 
artery. 

Common  intestinal 
lymphatic  trunk. 

Renal  artery. 

Renal  vein. 

Common  lumbar 
lymphatic  trunk. 


THORACIC  CAVITY  89 

outwards  it  ends  by  joining  the  internal  jugular  vein  at  its 
point  of  union  with  the  subclavian  vein.  In  the  diagrams 
which  are  given  of  the  posterior  and  superior  mediastinal 
spaces,  the  relations  of  the  thoracic  duct  may  be  studied 
(Figs.  44,  p.  81;  39,  p.  69;  38,  p.  68;  40,  p.  71).  It 
will  be  seen  that  in  the  posterior  mediastinum  it  lies 
behind  the  oesophagus,  but  in  the  superior  mediastinum  it  is 
placed  upon  the  left  side  of  the  oesophagus.  In  the  former 
situation,  before  the  parts  are  disturbed  by  dissection,  it  can 
readily  be  exposed  by  raising  the  right  lung  and  dividing  the 
right  mediastinal  pleura ;  in  the  latter  situation  the  left  lung 
must  be  raised  and  the  left  mediastinal  pleura  divided.  As 
it  passes  upwards  through  the  thorax,  the  thoracic  duct 
pursues  a  somewhat  wavy  or  flexuous  course.  It  frequently 
breaks  up  into  two  or  more  branches,  which  unite  again  to 
form  a  single  trunk.  It  is  provided  at  intervals  with  valves 
of  two  segments,  and  these,  when  the  duct  is  injected,  give 
it  a  beaded  or  nodulated  appearance.  The  valves  are  more 
especially  numerous  in  the  upper  part  of  the  duct. 

Thoracic  Lymphatic  Glands. — Throughout  the  dissection  of  the  thorax 
the  dissector  has,  from  time  to  time,  met  with  groups  of  lymphatic  glands. 
These  are  of  considerable  importance,  seeing  that  their  enlargement  in 
disease  is  not  infrequently  the  cause  of  serious  thoracic  trouble.  The 
following  are  the  chief  groups  : — (1)  Two  chains  of  minute  glands,  which 
are  placed  in  relation  to  the  anterior  thoracic  wall  and  follow  the  course  of 
the  internal  mammary  vessels.  They  are  termed  sternal  glands  (lympho- 
glandulae  sternales),  and  are  joined  by  lymphatic  vessels  from  the  anterior 
thoracic  wall,  the  mammary  glands,  the  front  part  of  the  diaphragm,  and 
the  upper  part  of  the  front  wall  of  the  abdomen.  (2)  Two  chains  of  glands 
on  the  posterior  thoracic  wall — one  on  either  side  of  the  spine  in  relation 
to  the  vertebral  extremities  of  the  ribs.  They  are  very  minute,  and  offsets 
from  these  chains  accompany  the  intercostal  vessels  between  the  intercostal 
muscles.  They  are  therefore  called  the  intercostal  glands  (lymphoglandulce 
intercostales),  and  they  receive  the  lymphatics  of  the  posterior  thoracic 
wall.  (3)  Anterior  mediastinal  glands  (lymphoglandulse  mediastinales 
anteriores),  two  or  three  in  number,  which  receive  lymphatics  from  the 
diaphragm  and  upper  surface  of  the  liver.  They  occupy  the  lower  open 
part  of  the  anterior  mediastinum.  (4)  Posterior  mediastinal  glands 
(lymphoglandulx  mediastinales  posteriores),  which  follow  the  course  of  the 
thoracic  aorta,  and  are  joined  by  lymphatics  from  the  diaphragm,  pericar- 
dium, and  'esophagus.  (5)  Superior  mediastinal  glands  (lymphoglandulce 
mediastinales  superiores),  an  important  group,  eight  to  ten  in  number,  and 
placed  in  relation  to  the  aortic  arch.  The  lymphatics  of  the  heart,  peri- 
cardium, and  thymus  body  enter  these.  (6)  Bronchial  glands  (lympho- 
glanduku  bronchiales),  continuous  above  with  the  preceding,  and  massed 
chiefly  in  the  interval  between  the  two  bronchi.  They  are  also  prolonged 
into  the  roots  of  the  lungs.  The  lymphatic  vessels  of  the  lungs  pour  their 
contents  into  them.  In  the  adult,  they  are  generally  dark  in  colour,  and 
sometimes  as  black  as  ink. 


qo  THORAX 

The  lymphatics  of  the  right  side  of  the  chest,  the  right  lung,  and  the 
right  half  of  the  heart  join  the  right  lymphatic  duct  (ductus  lymphaticus 
dexter),  a  minute  and  short  vessel  situated  in  the  root  of  the  neck.  It 
opens  into  the  angle  of  union  between  the  right  internal  jugular  and  right 
subclavian  veins. 

Removal  of  the  Lungs. — The  lungs  may  now  be  removed  by  dividing 
the  trachea  about  an  inch  and  a  half  above  its  bifurcation.  The  bronchi 
and  vessels  should  be  traced  into  the  lobes  of  the  lungs,  and  their  manner 
of  subdivision  and  distribution  throughout  its  substance  studied. 

Ramification  of  the  Bronchi  and  Vessels  within  the  Lungs. 

— The  student  has  previously  observed  that  the  two  lungs  are 
not  symmetrical.  The  right  lung  is  subdivided  into  three 
lobes,  whilst  the  left  lung  is  cleft  into  two  lobes.  The  bronchi 
exhibit  a  corresponding  want  of  symmetry.  Each  tube,  as  it 
approaches  the  pulmonary  hilum,  gives  off  branches  for  the 
different  lobes.  The  right  bronchus  sends  off  two  such 
branches  for  the  upper  and  middle  lobes  of  the  right  lung 
respectively,  whilst  the  main  stem  of  the  tube  sinks  into  the 
inferior  lobe.  The  left  bronchus  sends  off  a  large  branch  to 
the  upper  lobe  of  the  left  lung,  and  then  enters  the  lower 
lobe.  The  first  branch  of  the  right  bronchus  leaves  the  main 
stem  about  one  inch  from  the  trachea.  The  first  branch  of 
the  left  bronchus,  on  the  other  hand,  takes  origin  about  twice 
that  distance  from  the  trachea. 

The  relation  of  the  pulmonary  artery  to  the  bronchial 
subdivisions  is  different  on  the  two  sides.  In  both  cases  it 
lies  in  front  of  the  undivided  portion  of  the  tube,  but  on  the 
right  side  it  turns  backwards,  so  as  to  reach  the  posterior 
aspect  of  the  bronchus  below  the  first  and  above  the  second 
division.  It  is  due  to  this  arrangement  that  the  right  bronchus 
occupies  the  highest  level  in  the  right  pulmonary  root.  On 
the  left  side,  the  pulmonary  artery  turns  backwards  above  the 
level  of  the  first  bronchial  branch,  and  therefore  holds  the 
highest  place  in  the  left  pulmonary  root.  On  the  right 
side,  then,  the  first  bronchial  branch  is  placed  above  the 
pulmonary  artery,  and  it  is  termed  the  eparterial  bronchus  ; 
all  the  others  lie  below  it,  and  are  termed  hyparterial  bronchi. 
On  the  left  side  there  is  no  eparterial  tube ;  they  are  all 
hyparterial. 

When  the  main  stem  of  the  bronchus  is  followed  into  the 
inferior  lobe  on  either  side,  it  will  be  observed  to  travel  down- 
wards towards  the  back  part  of  the  base,  and  give  off,  as  it 
proceeds,  a   series  of  ventral,  and  a  series  of  smaller  dorsal 


THORACIC  CAVITY 


9i 


branches.  The  first  hyparterial  division  on  each  side  (i.e.  the 
branch  to  the  middle  lobe  of  the  right  side,  and  the  branch 
to  the  upper  lobe  of  the  left  side)  may  be  regarded  as  the 
first  member  of  the  ventral  group  (Fig.  48). 

It  should  be  observed  that  when  the  bronchial  tubes  enter 
the  lung,  they  cease  to  be  flattened  posteriorly,  and  become 
uniformly  cylindrical.  This  is  due  to  the  cartilage  being 
disposed  around  the  tube  on   all  its  aspects,  in  the  form   of 


-Schema  of  the  Branching  of  the  Two  Bronchi. 
(From  Gegenbaur. ) 

P.  Pulmonary  artery  ;  d.  Dorsal  divisions  of  the  bronchi ;  v.  Ventral  divisions 
of  the  bronchi.  The  highest  ?<  on  each  side  indicates  the  first  hyparterial 
bronchus,  or,  in  other  words,  the  branch  to  the  upper  lobe  of  the  left  lung 
and  the  middle  lobe  on  the  right  lung. 


irregular  flakes,  and  imperfect  rings.  The  farther  the  tubes 
are  traced,  the  scarcer  and  finer  become  the  particles  of 
cartilage. 

The  pulmonary  vessels  in  the  substance  of  the  lungs  run 
with  the  bronchi.  The  veins  still  keep  to  the  front  of  the 
air-passages ;  the  arteries,  however,  as  we  have  noted,  turn 
backwards  to  reach  their  posterior  aspect,  and  this  relation 
they  maintain  in  the  lung  substance. 


92  THORAX 

Dissection. — The  dissector  should  next  turn  his  attention  to  the  thoracic 
portion  of  the  sympathetic  nervous  system.  In  order  to  expose  it,  he 
must  strip  the  parietal  pleura  from  the  sides  of  the  vertebrae  and  the  inner 
surface  of  the  ribs. 

Gangliated  Cord  of  the  Sympathetic  (pars  thoracicalis 
nervi  sympathici). — This  extends  downwards  through  the 
thoracic  cavity  upon  the  heads  of  the  ribs  and  the  interven- 
ing intercostal  spaces,  and  has  an  appearance  somewhat 
similar  to  that  of  a  knotted  string.  The  thoracic  ganglia  are 
usually  eleven  in  number.  For  the  most  part  these  lie  on 
the  heads  of  the  ribs,  but  the  first  is  placed  over  the  inner 
part  of  the  first  intercostal  space.  Towards  the  diaphragm 
the  cord  inclines  forward,  so  that  one  or  two  of  the  lower 
ganglia  come  to  lie  upon  the  bodies  of  the  dorsal  vertebrae. 
The  first  ganglion  is  considerably  larger  than  those  which 
succeed  it.  They  are  all  linked  together  by  intervening  nerve 
cords.  Superiorly,  the  thoracic  part  of  the  sympathetic  is 
continuous  with  the  cervical  sympathetic ;  whilst  inferiorly  it 
becomes  continuous  with  the  abdominal  portion  of  the  sym- 
pathetic by  passing  behind  the  ligamentum  arcuatum  internum 
of  the  diaphragm. 

The  branches  which  spring  from  the  ganglia  may  be 
divided  into  two  sets :  (a)  central  communicating  and  (b) 
peripheral  branches  of  distribution. 

Central  Communicating  Branches. — One  of  the  leading 
characters  of  the  thoracic  portion  of  the  sympathetic  cord  is 
the  intimate  manner  in  which  it  is  brought  into  connection 
with  the  spinal  nerves.  White  rami  communicantes  pass  from 
each  of  the  intercostal  nerves  into  the  sympathetic  cord. 
They  become  connected  either  with  the  ganglia  or  with  the 
intervening  portions  of  the  cord.  G?~ey  rami  conwiunicantes, 
on  the  other  hand,  arise  from  each  ganglion,  somewhat 
irregularly,  and  convey  fibres  to  the  various  intercostal  nerves. 

Peripheral  Branches  of  Distribution. — These  take  origin 
irregularly,  and  are  (i)  pulmonary,  (2)  aortic,  and  (3)  the 
three  splanchnic  nerves. 

The  pulmonary  branches  spring  from  the  second,  third,  and 
fourth  ganglia,  and  join  the  posterior  pulmonary  plexus.  The 
aortic  branches  are  fine  filaments  which  arise  from  the  upper 
five  ganglia  and  proceed  to  the  coats  of  the  thoracic  aorta. 

The  splanchnic  nerves  are  three  in  number,  and  are  dis- 
tinguished by  the  terms,  great,  small,  and  smallest,  and  they 
are  destined  for  the  supply  of  abdominal  viscera. 


THORACIC  CAVITY  93 

The  great  splanchnic  nerve  (nervus  splanchnicus  major)  is 
formed  by  the  union  of  five  roots  derived  from  the  sixth, 
seventh,  eighth,  ninth,  and  tenth  ganglia.  This  description, 
however,  must  be  regarded  as  being  somewhat  arbitrary,  as 
there  is  a  considerable  amount  of  variability  in  the  number 
and  manner  of  origin  of  the  roots  of  this  nerve.  The  great 
splanchnic  has  more  the  appearance  of  a  cerebro-spinal 
nerve  than  a  sympathetic  nerve,  owing  to  the  large  number 
of  spinal  nerve-fibres  which  it  contains.  It  passes  down- 
wards upon  the  bodies  of  the  vertebrae,  and  leaves  the  thorax 
by  piercing  the  crus  of  the  diaphragm.  Within  the  abdomen 
it  ends  by  joining  the  upper  part  of  the  semilunar  ganglion. 

Upon  the  last  dorsal  vertebra,  a  ganglion  called  the  splanchnic  ganglion 
will  in  all  probability  be  found  in  connection  with  the  great  splanchnic 
nerve.  This  ganglion  is  usually  of  small  size,  involving  only  a  very  few 
of  the  anterior  fibres  of  the  nerve.  Sometimes,  however,  it  forms  a  dis- 
tinct oval  bulging  on  the  nerve-trunk.  A  few  slender  filaments  are  given 
by  the  ganglion  to  the  coats  of  the  aorta,  and  these  in  some  cases  may  be 
made  out  to  communicate  across  the  middle  line  of  the  body  with  the 
corresponding  branches  of  the  ganglion  of  the  opposite  side. 

The  small  splanchnic  nerve  (nervus  splanchnicus  minor) 
arises  by  two  roots  from  the  ninth  and  tenth  or  from  the  tenth 
and  eleventh  thoracic  ganglia.  It  enters  the  abdomen  by 
piercing  the  crus  of  the  diaphragm,  and  it  ends  by  joining 
the  lower  part  of  the  semilunar  ganglion. 

The  smallest  sftlatichnic  nerve  (nervus  splanchnicus  imus) 
is  a  minute  twig  which  takes  origin  from  the  lowest  thoracic 
ganglion.  It  pierces  the  diaphragm,  and  ends  in  the  renal 
plexus.  It  is  often  absent,  and  then  its  place  is  taken  by  one 
or  more  filaments  from  the  small  splanchnic  nerve. 

To  obtain  a  proper  view  of  this  minute  nerve,  the  diaphragm  should 
be  divided  over  its  course,  but  this  can  only  be  done  in  cases  where  the 
dissector  of  the  abdomen  has  completed  his  examination  of  the  diaphragm. 

Thoracic  Wall. — The  thoracic  wall  should  now  be  studied 
from  within.  Certain  facts  which  have  previously  been 
stated  regarding  it  can  now  be  verified  (p.  4).  The  internal 
intercostal  ??iuscle,  in  each  space,  will  be  seen  to  extend 
backwards  as  far  as  the  angles  of  the  ribs.  At  this  point 
it  stops  abruptly,  but  the  external  intercostal  muscle  is  not 
exposed  to  view.  It  is  covered  on  its  deep  aspect  by  the 
posterior  intercostal  membrane,  the  connexions  of  which  can 
now  be  ascertained. 


94  THORAX 

The  posterior  i?itercostal  membrane  is  a  strong  aponeurotic 
layer  which  is  continuous  internally  with  the  outer  margin  of 
the  superior  costo-transverse  ligament,  and  extends  outwards 
upon  the  deep  surface  of  the  external  intercostal  muscle.  At 
the  inner  margin  of  the  internal  intercostal  muscle  it  passes 
between  the  two  intercostal  muscular  strata  and  is  gradually 
lost.  The  intercostal  vessels  and  nerve  extend  outwards 
upon  its  anterior  aspect  under  cover  of  the  pleura. 

The  subcostal  muscles  are  also  displayed.  They  are  small 
fleshy  fasciculi  placed  upon  the  ribs,  internal  to  their  angles. 
The  muscular  fibres  which  compose  them  have  the  same 
direction  as  the  internal  intercostal  muscles.  They  extend 
over  one  or,  in  many  cases,  two  intercostal  spaces. 

Dissection. — -Remove  the  posterior  intercostal  membrane  from  one  or 
two  of  the  spaces,  and  the  subjacent  external  intercostal  muscles  will  be 
brought  into  view.  These  muscles  reach  backwards  as  far  as  the  tubercles 
of  the  ribs. 

Intercostal  Arteries. — The  aortic  intercostal  arteries  have 
already  been  seen  taking  origin  from  the  thoracic  aorta. 
One  is  given  to  each  of  the  nine  lower  intercostal  spaces 
upon  both  sides  of  the  body.  As  the  aorta  lies  somewhat  to 
the  left  of  the  middle  line,  the  right  aortic  intercostal  arteries 
are  longer  than  those  of  the  left  side.  In  both  cases  they 
run  outwards  over  the  bodies  of  the  vertebrae,  and  under 
cover  of  the  gangliated  cord  of  the  sympathetic.  On  the 
right  side,  the  arteries  also  pass  under  cover  of  the  oesophagus, 
the  thoracic  duct,  and  the  vena  azygos  major.  As  they  leave 
the  vertebral  column  to  enter  the  intercostal  spaces,  each  of 
the  vessels  gives  off  a  large  dorsal  bra?ich  which  passes  back- 
wards in  the  interval  between  the  transverse  processes  and  is 
distributed  to  the  muscles  and  skin  of  the  back.  From  this 
branch  a  spinal  twig  is  supplied  through  the  intervertebral 
foramen  to  the  spinal  cord  and  its  membranes.  In  each 
space,  the  intercostal  artery  proceeds  outwards,  first  lying 
between  the  posterior  intercostal  membrane  and  the  pleura, 
and  afterwards  between  the  two  muscular  strata.  Each 
artery  is  accompanied  by  a  nerve  and  a  vein.  The  vein 
usually  occupies  the  highest  level,  the  nerve  the  lowest  level, 
whilst  the  artery  is  intermediate.  The  distribution  of  these 
vessels  in  the  thoracic  parietes  has  already  been  studied 
(p.  6). 

The   position   of  the   intercostal  artery  in   the  intercostal 


THORACIC  CAVITY  95 

space  is  a  matter  of  some  surgical  importance.  At  first  it 
crosses  the  intercostal  space  obliquely,  so  as  to  gain  the 
shelter  of  the  subcostal  groove  of  the  rib  which  bounds  the 
space  above.  It  attains  this  position  near  the  angle  of  the 
rib,  and  as  it  proceeds  forwards  the  groove  affords  it  a  very 
efficient  protection  against  wounds  from  without. 

The  intercostal  arteries  which  supply  the  two  highest 
intercostal  spaces  are  derived  from  the  superior  intercostal 
branch  of  the  subclavian  artery.  The  superior  intercostal 
artery  descends  upon  the  necks  of  the  first  two  ribs,  and 
external  to  the  gangliated  cord.  It  anastomoses  with  the  first 
aortic  intercostal  artery,  and  sends  outwards  two  vessels  for 
the  two  highest  spaces.  Each  of  these,  in  turn,  gives  off  a 
dorsal  branch  similar  to  the  dorsal  branches  of  the  aortic 
intercostal  arteries. 

Subcostal  Arteries. — These  arteries  form  a  pair  of  vessels 
in  series  with  the  intercostal  arteries.  They  enter  the  abdomen 
by  passing  under  the  ligamentum  arcuatum  externum,  and 
run  in  company  with  the  last  dorsal  nerves  along  the  lower 
borders  of  the  last  pair  of  ribs. 

Intercostal  Nerves. — The  intercostal  nerves  pass  outwards 
in  company  with  the  arteries.  The  connecting  twigs  which 
pass  between  these  nerves  and  the  sympathetic  ganglia  have 
already  been  noted.  Each  nerve  lies  at  a  lower  level  than 
the  corresponding  artery,  and  is  at  first  placed  between  the 
posterior  intercostal  membrane  and  the  pleura,  and  then 
between  the  two  muscular  strata.  The  further  course  of  these 
nerves  is  described  at  p.  5. 

The  first  dorsal  nerve  will  be  found  passing  upwards  over 
the  neck  of  the  first  rib  to  join  the  brachial  plexus.  It  gives 
a  small  branch  to  the  first  intercostal  space,  but  this  nerve, 
although  it  is  disposed  after  the  manner  of  an  intercostal 
nerve,  does  not  furnish,  as  a  rule,  a  lateral  cutaneous  or  an 
anterior  branch.  The  second  dorsal  or  intercostal  nerve,  as  a 
rule,  sends  a  branch  upwards  over  the  neck  of  the  second  rib 
to  join  that  portion  of  the  first  dorsal  nerve  which  enters  the 
brachial  plexus.  This  communicating  twig  is  usually  minute 
and  insignificant,  but  sometimes  it  is  a  large  nerve ;  and,  in 
these  cases,  the  intercosto-humeral  nerve,  or  lateral  cutaneous 
branch  of  the  second  intercostal  nerve,  is  very  small  or 
altogether  absent. 

Veins   of  the   Thoracic   Wall. — When   the    dissector    has 


96  THORAX 

traced  the  intercostal  veins  to  their  various  destinations,  he 
will  find  that  they  differ  in  their  arrangement  upon  the  two 
sides  of  the  body.  On  the  right  side  they  terminate  in  three 
different  ways  : — 

1.  The  intercostal  vein   of  the   first  or   highest   space  joins  the   right 

innominate  vein  (sometimes  the  vertebral  vein). 

2.  The  intercostal  veins  of  the  second  and  third  spaces  (and  sometimes 

of  the  fourth  space)  unite  into  a  common  trunk,  which  joins  the 
upper  part  of  the  vena  azygos  major.  The  common  trunk  is 
termed  the  superior  intercostal  vein. 

3.  The  intercostal  veins  of  the  eight  lower  spaces  join  the  vena  azygos 

major. 

On  the  left  side  of  the  body  four  modes  of  termination  may 
be  recognised : — 

1.  The  intercostal  vein  of  the  first  or  highest  space  has  the  same  termina- 

tion as  the  corresponding  vein  of  the  right  side.  It  joins  the  left 
innominate  vein  (sometimes  the  vertebral  vein  of  its  own  side). 

2.  The  intercostal  veins  of  the  second  and  third  spaces  (and  sometimes 

of  the  fourth  space)  converge,  and  by  their  union  form  a  single 
trunk,  termed  the  superior  intercostal  vein,  which  crosses  the  arch 
of  the  aorta  and  joins  the  left  innominate  vein  independently  of 
the  first  intercostal  vein. 

3.  The  intercostal  veins  of  the  fourth,  fifth,  sixth,  seventh,  and  eighth 

spaces  terminate  in  the  vena  azygos  minor  superior. 

4.  The  intercostal  veins  of  the  ninth,  tenth,  and  eleventh  spaces  join  the 

vena  azygos  minor  inferior. 

The  azygos  veins  which  thus  receive  the  blood  of  the  great 
majority  of  the  intercostal  veins  should  now  be  studied. 

Vena  Azygos  Major  (vena  azygos). — This  vein  takes  origin 
within  the  abdomen  in  the  right  ascending  lumbar  veiti  (vena 
lumbalis  ascendens),  a  vessel  which  links  together  certain  of 
the  lumbar  veins,  and  sometimes  presents  a  direct  communica- 
tion with  the  common  iliac  vein.  It  enters  the  thorax  through 
the  aortic  opening  of  the  diaphragm,  lying  upon  the  right  side 
of  the  thoracic  duct  and  the  aorta.  In  the  thorax  it  extends 
upwards  upon  the  bodies  of  the  dorsal  vertebrae  and  over 
the  right  intercostal  arteries,  until  it  reaches  the  level  of  the 
upper  border  of  the  root  of  the  right  lung.  At  this  point  it 
hooks  forwards  over  the  right  bronchus,  and  ends  by  joining 
the  superior  vena  cava.  It  is  situated  in  the  posterior 
mediastinum,  with  the  aorta  and  thoracic  duct  lying  to  the 
left  (Fig.  47,  p.  38). 

The  tributaries  of  the  vena  azygos  major  are  as  follows  : — 
(1)  the  superior  intercostal  vein  of  the  right  side;  (2)  the 
intercostal  veins  of  the  eight  lower  spaces  of  the  right  side ; 


THORACIC   CAVITY  97 

(3)  the  vena  azygos  minor  superior;  (4)  the  vena  azygos 
minor  inferior ;  (5)  the  bronchial  veins  from  the  right  lung  ; 
(6)  certain  of  the  oesophageal  veins;  (7)  some  minute 
pericardiac  veins. 

The  vena  azygos  major  communicates  below  with  some  of 
the  lumbar  veins — tributaries  of  the  inferior  vena  cava  ;  whilst 
above,  it  pours  its  blood  into  the  superior  vena  cava.  In  this 
way  it  forms  a  link  by  which  the  superior  vena  cava  is  brought 
into  connection  with  the  inferior  vena  cava. 

Vena  Azygos  Minor  Superior  (vena  hemiazygos  accessoria). 
— This  vein  is  formed  on  the  left  side  of  the  body  by  the  union 
of  the  intercostal  veins  of  the  fourth,  fifth,  sixth,  seventh,  and 
eighth  spaces.  It  communicates  above  with  the  left  superior 
intercostal  vein,  which  carries  the  blood  from  the  second  and 
third  intercostal  spaces  to  the  left  innominate  vein.  At  the 
level  of  the  eighth  dorsal  vertebra  it  turns  inwards  behind  the 
aorta  and  thoracic  duct,  and  crossing  the  middle  line  ends 
by  joining  the  vena  azygos  major.  In  many  cases,  however, 
it  joins  the  vena  azygos  minor  inferior.  In  addition  to  the 
intercostal  veins  it  receives  the  left  bronchial  veins. 

Vena  Azygos  Minor  Inferior  (vena  hemiazygos). — This 
vein  takes  origin  within  the  abdomen  as  the  left  ascending 
lumbar  vein.  It  enters  the  thorax  by  piercing  the  left  crus  of 
the  diaphragm,  and  is  continued  upwards  upon  the  vertebral 
column  as  far  as  the  ninth  dorsal  vertebra.  At  this  point  it 
turns  to  the  right,  and  crossing  behind  the  aorta  and  the 
thoracic  duct,  it  joins  the  vena  azygos  major  independently  of 
the  vena  azygos  minor  superior. 

The  tributaries  of  this  vein  are  the  intercostal  veins  of  the 
three  lower  spaces  of  the  left  side. 

The  veins  of  the  thoracic  parietes  are  extremely  variable,  and  the  above 
description  of  them  must  be  looked  upon  as  merely  representing  their  more 
usual  arrangement. 


THORACIC  JOINTS. 

The  student  should  now  complete  the  dissection   of  the 
thorax  by  an  examination  of  the  various  thoracic  joints. 

Dissection. — -The  portion  of  the  Sternum  with  the  cartilages  of  the  ribs 
which  was  laid  aside,  together  with  the  other  joints  in  connection  with  the 
anterior  wall  of  the  thorax,  should  now  be  dissected.      Inter-sternal,  costo- 

vor..  n — 7 


98  THORAX 

sternal,  and  inter-chondral  articulations  require  examination.  Very  little 
dissection  is  necessary.  After  the  ligaments  have  been  defined,  the  dissector 
should  remove  a  thin  slice  from  the  anterior  aspect  of  each  articulation,  in 
order  that  the  interior  of  the  joint  may  be  displayed. 

Manubrio-gladiolar  Articulation. — This  joint,  between  the 
manubrium  and  the  gladiolus  of  the  sternum,  partakes  of  the 
nature  of  an  amphiarthrosis.  The  opposing  surfaces  of  bone 
are  covered  by  a  layer  of  hyaline  cartilage,  and  are  united  by 
intermediate  fibro-cartilage.  The  joint  is  supported  by  some 
anterior  and  posterior  longitudinal  fibres  which  are  developed 
in  connection  with  the  strong  and  thick  periosteum.  The 
posterior  ligament  is  the  stronger  of  the  two. 

Sterno- chondral  Articulations.  —  Seven  ribs  articulate,  by 
means  of  their  cartilages,  directly  with  each  side  of  the 
sternum.  The  articulations  of  the  first  and  the  sixth  are 
peculiar,  inasmuch  as  they  articulate  with  single  pieces  of  the 
sternum,  viz.,  with  the  manubrium  and  the  lowest  piece  of  the 
gladiolus  respectively,  whereas  each  of  the  cartilages  of  the 
other  true  ribs  articulates  with  two  segments  of  the  sternum. 
The  cartilage  of  the  first  rib  is  implanted  upon  the  side  of  the 
manubrium  without  any  synovial  membrane,  or  other  material, 
intervening.  The  second  costal  cartilage  is  usually  separated 
from  the  sternum  by  two  synovial  membranes,  between  which 
an  interarticular  ligament  is  developed.  In  the  case  of  the 
other  joints  it  is  more  common  to  find  a  single  synovial  cavity 
and  no  interarticular  ligament.  There  is,  however,  considerable 
variety  in  these  articulations,  and  a  synovial  membrane  is  very 
frequently  wanting  altogether  in  the  sterno-chondral  joint  of 
the  seventh  costal  cartilage. 

With  the  exception  of  the  first,  and  very  frequently  the 
seventh,  the  sterno-chondral  joints  belong  to  the  diarthrodial 
variety.  They  are  provided  with  anterior  and  posterior 
ligaments,  and  also,  in  those  cases  where  the  joint  presents  a 
double  synovial  cavity,  with  an  interarticular  ligament. 

The  anterior  and  posterior  liga?ne?its  (ligamenta  sterno-costalia 
radiata)  are  strong,  flattened  bands  of  fibres  which  radiate 
from  the  extremities  of  the  rib-cartilages,  and  blend  with  the 
periosteum  on  the  anterior  and  posterior  surfaces  of  the 
sternum.  The  interarticular  ligaments  are  feeble  bands  which 
pass  from  the  tips  of  the  rib-cartilages  to  the  sternum,  and 
divide  the  articulations  in  which  they  exist  into  an  upper  and 
a  lower  compartment,  each  lined  by  a  synovial  membrane. 


THORACIC  JOINTS 


99 


Inter-chondral  Articulations. — These  joints  are  formed 
between  the  adjacent  margins  of  the  costal  cartilages  of  some 
of  the  lower  ribs  (generally  from  the  fifth  or  sixth  to  the  ninth). 
They  are  protected  by  capsules  formed  by  strong  oblique 
ligamentous  fibres,  and  are  lined  by  synovial  membranes. 

Costo-vertebral  Articulations. — With  the  exception  of  the 
first  and  the  last  three  ribs,  the  head  of  each  rib  articulates 
with  the  bodies  of  two  vertebrae  and  the  intervening  inter- 
vertebral substance  (articulatio  capituli   costae).     The  costal 


Anterior  common  ligament 


Rib 


lips  \ 


Three  si 
of  stellate-1 
ligament  I 


Superior 
costo-transverse 
^  ligament 


Fig.  49. — Costo-vertebral.  Joints  as  seen  from  the  front  ;   also  Anterior 
Common  Ligament  of  Vertebral  Column. 

head  is  wedge-shaped,  and  the  socket  formed  for  its  reception 
presents  a  corresponding  form.  From  the  intervertebral  disc 
taking  part  in  the  formation  of  the  socket,  a  certain  amount 
of  elasticity  is  communicated  to  the  joint,  and  shocks  given  to 
the  thoracic  wall  are  the  more  successfully  counteracted.  The 
heads  of  the  first,  tenth,  eleventh,  and  twelfth  ribs  are  implanted 
directly  upon  the  bodies  of  the  corresponding  vertebrae, 
although  in  the  case  of  the  first  rib  the  intervertebral  disc 
immediately  above  also,  as  a  rule,  takes  a  considerable  share 
in  the  formation  of  its  socket.  The  articulations  between  the 
heads  of  the  ribs  and  the  bodies  of  the  vertebrae  are  termed 
the  capitular  joints  (articulationes  capitulorum). 


ioo  THORAX 

But  the  vertebral  extremities  of  the  ribs  present  another 
series  of  articulations.  The  upper  ten  ribs,  by  means  of  their 
tubercles,  rest  upon  and  articulate  with  the  extremities  of  the 
transverse  processes  of  the  corresponding  dorsal  vertebrae. 
These  joints  are  termed  the  costo  -  transverse  articulations 
(articulationes  costo-transversariae).  The  eleventh  and  twelfth 
ribs  have  no  tubercles,  and  do  not  articulate  with  the 
transverse  processes  of  the  vertebrae  with  which  they  are 
connected. 

Capitular  Joints. — These  joints  b.elong  to  the  diarthrodial 
variety,  and  are  provided  with  —  (i)  an  anterior  capitular 
ligament ;  (2)  an  interarticular  ligament ;  and  (3)  two 
synovial  membranes.  In  the  case  of  the  four  ribs,  however, 
which  articulate  with  the  body  of  one  vertebra  alone  (viz.,  the 
first,  tenth,  eleventh,  and  twelfth),  the  joint  cavity  is  single. 

The  anterior  capitular  or  stellate  ligament  (ligamentum 
capituli  costae  radiatum)  is  placed  in  front  of  the  joint.  It  is 
composed  of  strong  fibres,  which  radiate  in  a  fan-shaped 
manner  from  the  head  of  the  rib.  Its  vertebral  attachment 
is  effected  by  three,  more  or  less  distinct,  slips — (1)  the 
uppermost,  which  is  the  largest,  passes  upwards  and  inwards 
to  the  body  of  the  vertebra,  which  forms  the  upper  part  of 
the  socket  for  the  head  of  the  rib ;  (2)  the  middle  slip  is 
attached  to  the  intervertebral  disc ;  and  (3)  the  lowest  slip 
goes  to  the  body  of  the  vertebra  below  the  head  of  the  rib. 
The  part  of  the  joint  uncovered  by  the  stellate  ligament  is 
surrounded  by  short  fibres  which  form  a  capsule ;  enclosing  the 
synovial  membranes. 

In  the  four  joints  in  which  the  head  of  the  rib  is  in 
contact  with  the  body  of  one  vertebra,  the  stellate  ligament  is 
composed  of  only  two  slips.  Of  these,  the  lower  is  attached 
to  the  body  of  the  vertebra  which  supports  the  rib,  whilst  the 
upper  passes  upwards  to  the  lower  border  of  the  vertebral 
body  immediately  above. 

Dissection. — The  interarticular  ligament  may  be  exposed  by  removing 
the  stellate  ligament  from  the  front  of  the  joint. 

The  interarticular  ligament  of  the  capitular  joints  is 
composed  of  short  strong  fibres  which  are  attached,  on  the 
one  hand,  to  the  ridge  between  the  two  articular  facets  on  the 
head  of  the  rib,  and  on  the  other  hand  to  the  intervertebral 
disc.      It  divides  the  joint  into  two  synovial  cavities,  and  it  is 


THORACIC  JOINTS  101 

absent  in  those  cases  in  which  the  head  of  the  rib  articulates 
with  the  body  of  one  vertebra. 

The  synovial  membranes  are  two  in  number,  except  in  the 
capitular  joints  of  the  first  and  last  three  ribs.  One  is  placed 
above,  and  the  other  below  the  interarticular  ligament. 

Costo-transverse  Articulations. — These  are  provided  with 
capsular  ligaments,  and  with  superior,  middle,  and  posterior 
costo-transverse  ligaments.  Each  joint  cavity  is  lined  by  a 
synovial  membrane. 

The  superior  costo-transverse  ligament  (ligamentum  costo- 
transversarium  anterius)  passes  obliquely  downwards  and 
inwards  from  the  lower  border  of  the  transverse  process  to 
the  upper  border  of  the  neck  of  the  rib  next  below  it.  Its 
internal  margin  is  thick  and  well  defined,  and  its  outer  border 
becomes  continuous  with  the  posterior  intercostal  membrane. 

The  interosseous  costo-transverse  ligament  (ligamentum  costo- 
transversarium  posterius)  consists  of  fibrous  bands  .which  pass 
between  the  neck  of  the  rib  and  the  anterior  surface  of  the 
transverse  process  against  which  it  rests. 

The  fibres  of  this  ligament  are  so  short  that  it  is  exceedingly  difficult  to 
obtain  a  proper  view  of  them.  The  best  plan  is  to  saw  off,  in  a  horizontal 
direction,  the  upper  parts  of  the  neck  of  the  rib  and  the  transverse  process 
to  which  it  is  attached. 

The  posterior  costo-transverse  ligament  (ligamentum  tuberculi 
costae)  is  a  strong  flattened  band  which  passes,  on  the  posterior 
aspect  of  the  joint,  from  the  tip  of  the  transverse  process  to 
the  rough  portion  of  the  tubercle  of  the  rib. 

The  posterior  costo-transverse  ligament,  supplemented  by 
a  few  fibres  which  surround  the  synovial  membrane  of  the 
joint,  forms  the  capsular  ligament.  When  the  posterior  costo- 
transverse ligament  is  removed,  the  synovial  membrane  is 
displayed. 

Intervertebral  Articulations. — The  bodies  of  the  vertebrae 
are  held  together  by  a  series  of  amphiarthrodial  joints, 
supported  in  front  by  an  anterior  common  ligament,  and 
behind  by  a  posterior  common  ligament.  The  neural  arches, 
by  means  of  the  articular  processes,  form  a  series  of  diarthrodial 
joints  surrounded  by  capsular  ligaments,  and  lined  by  synovial 
membranes.  ( Certain  ligaments  pass  between  different  portions 
of  the  neural  arches  and  their  processes,  viz.,  the  ligamenta 
subflava  between  adjacent  laminae,  the  inter-transverse,  the 
inter-spinous,  and  the  supra-spinous  ligaments. 


102 


THORAX 


Pedicle  of 
vertebra  (cut) 


Posterior 

common 
ligament 


The  laminae  and  the  spinous  processes  of  the  vertebrae  have  been 
removed  by  the  dissector  of  the  head  and  neck  in  opening  up  the  spinal 
canal  to  display  the  spinal  cord.  Consequently,  the  ligamenta  subflava, 
the  inter-spinous  and  supra-spinous  ligaments,  cannot  be  seen  at  present. 

The  anterior  common  ligament  (ligamentum  longitudinale 
anterius)  is  situated  in  front  of  the  bodies  of  the  vertebrae, 
and  extends  from  the  axis  vertebra  above  to  the  first  piece 
of  the  sacrum  below.  It  consists  of  stout  glistening  fibrous 
bands,  which  are  firmly  attached  to  the  margins  of  the  verte- 
bral bodies  and  to  the  intervertebral  discs.  The  most  super- 
ficial fibres  are  the  longest, 
and  extend  from  a  given 
vertebra  to  the  fourth  or 
fifth  below  it.  The  deeper 
fibres  have  a  shorter  course, 
and  pass  between  the  borders 
of  two,  three,  or  four  ad- 
jacent vertebrae.  The  dis- 
sector cannot  fail  to  notice 
that  the  origin  of  the  longus 
colli  muscle  is  inseparably 
connected  with  this  liga- 
ment. 

The  posterior  common 
ligament  (ligamentum  longi- 
tudinale posterius)  is  placed 
on  the  back  of  the  vertebral 
bodies,  and  therefore  within 
the  spinal  canal.  It  is  firmly 
Fig.  50. —Posterior  Common  Ligament  connected  to  the  margins  of 
of  the  Vertebral  Column.      The  neural     .«.  ,    1       ■,  1      j-         „      1   .„ 

,      ,        ,  ,  f .,      the  vertebral  bodies,  and  to 

arches   have   been   removed   from    the  \ 

vertebrae.  the  intervertebral  discs,  but 

is  separated  from  the  central 
parts  of  the  bodies  by  some  loose  connective  tissue  and  by  a 
plexus  of  veins.  It  is  constricted  where  it  covers  this  venous 
plexus,  but  widens  out  opposite  the  intervertebral  discs.  It 
therefore  presents  a  scalloped  or  denticulated  appearance. 

The  intervertebral  substance  (fibro-cartilago  intervertebralis) 
is  disposed  between  the  vertebras  in  a  series  of  flattened  discs 
of  white  fibro-cartilage  which  correspond  in  outline  to  the 
vertebrae  between  which  they  are  situated.  The  peripheral 
part  of  each  disc  is  tough  and  fibrous  (annulus  fibrosus),  the 


Inter- 
vertebral 
disc 


THORACIC  JOINTS  103 

central  portion  soft  and  pulpy  (nucleus  pulposus).  In  a 
transverse  section  the  peripheral  portion  appears  concentrically 
laminated  :  in  a  vertical  section  the  most  peripheral  laminae 
are  seen  to  be  bent  with  the  convexity  turned  away  from  the 
centre  of  the  disc,  the  most  central  laminae  to  be  bent  in  the 
opposite  direction,  and  the  intermediate  laminae  to  be  nearly 
straight.  It  will  be  easily  seen  that  this  remarkable  arrange- 
ment increases  the  elasticity  of  the  spine,  and  tends  to  restore 
it  to  its  natural  curvature  after  it  has  been  deflected  by  mus- 
cular action. 

The  intervertebral  discs  constitute  the  main  bond  of  union 
between  the  bodies  of  the  vertebrae,  but,  except  in  old  people, 
they  are  not  directly  attached  to  the  bone.  A  thin  layer  of 
encrusting  hyaline  cartilage  coats  the  opposing  vertebral 
surfaces. 

Vertical  and  transverse  sections  must  be  made  through  two  or  more  of 
the  intervertebral  discs,  in  order  that  their  structure  may  be  displayed. 

The  facets  of  the  articular  processes  are  coated  by  hyaline 
cartilage.  A  capsular  ligament  lined  by  a  synovial  membrane 
encloses  each  joint. 

The  intertransverse  ligaments  are  feeble  bands  which  pass 
between  the  tips  of  the  transverse  processes.  In  the  lower 
part  of  the  dorsal  regions  they  are  intimately  blended  with 
the  intertransverse  muscles  :  in  the  middle  and  upper  parts 
of  the  dorsal  region  they  entirely  replace  the  muscles. 


io4  HEAD  AND  NECK 


HEAD    AND    NECK. 

The  dissector  of  the  Head  and  Neck  begins  work  on  the 
same  day  that  the  subject  is  brought  into  the  dissecting-room. 
It  is  placed  on  a  short  table  for  this  purpose;  and  of  the 
two  days  during  which  it  remains  in  the  lithotomy  position, 
the  first  should  be  devoted  to  the  dissection  of  the  scalp,  and 
the  second  to  the  removal  of  the  brain. 


SCALP. 

Strictly  speaking,  the  term  "  scalp  "  should  be  restricted  to 
the  soft  parts  which  cover  the  vault  of  the  cranium  above  the 
level  of  the  temporal  ridges  and  the  superior  curved  line  of 
the  occipital  bone,  but  it  is  convenient  to  dissect  at  the  same 
time  the  superficial  structures  in  the  temporal  regions. 

Above  the  level  of  the  temporal  ridges  we  meet  with  five 
strata  as  we  dissect  from  the  surface  to  the  bone,  viz. — (i) 
the  skin  ;  (2)  the  superficial  fascia ;  (3)  the  occipito-frontalis 
muscle,  with  its  extensive  epicranial  aponeurosis ;  (4)  a  layer 
of  loose  areolar  tissue;  and  (5)  the  periosteum,  which  is  here 
termed  the  pericranium. 

Below  the  level  of  the  temporal  ridges  additional  structures 
are  observed  coating  the  cranium.  As  many  as  eight  layers 
may  be  recognised,  viz. — (1)  skin;  (2)  superficial  fascia;  (3) 
the  small  extrinsic  muscles  of  the  ear ;  (4)  the  thin  lateral 
part  of  the  epicranial  aponeurosis  ;  (5)  a  thin  layer  of  fascia 
descending  from  the  temporal  ridge  to  the  pinna ;  (6)  the 
temporal  fascia  ;  (7)  the  temporal  muscle  ;  (8)  the  periosteum. 

The  scalp  is  richly  supplied  with  both  nerves  and  blood- 
vessels. 

Dissection. — The  dissector  should  place  a  block  under  the  head  so  as  to 
raise  it  to  a  convenient  height,  and  proceed  with  the  dissection. 

Three  incisions  through  the  skin  are  required,  viz. — (1)  from  the  root 
of  the  nose  along  the  middle  line  of  the  cranium,  to  a  point  a  little  beyond 
the  external  occipital  protuberance  ;  (2)  from  the  tip  of  the  mastoid  process 
on  one  side,  over  the  summit  of  the  head  to  a  corresponding  point  upon 
the  opposite  side  ;  (3)  from  a  point  on  the  latter  incision  immediately  above 
the  pinna  on  each  side  downwards  in  front  of  the  auricle  to  the  root  of  the 


SCALP  105 

zygoma.  Four  flaps  of  skin  are  thus  marked  out,  and  these  should  be 
carefully  raised  from  the  subjacent  superficial  fascia.  This,  however,  is 
no  easy  matter,  owing  to  the  very  firm  connection  which  exists  between 
them.  The  roots  of  the  hair  which  pierce  the  integument  obliquely,  and 
are  embedded  in  the  superficial  fascia,  add  another  difficulty  to  the  proper 
reflection  of  the  integument. 

Superficial  Fascia. — On  the  summit  of  the  cranium  the 
superficial  fascia,  although  thin,  is  exceedingly  dense  and 
tough,  owing  to  strong  septa  of  fibrous  tissue  which  bind  it 
on  the  one  hand  to  the  integument,  and  on  the  other  to  the 
subjacent  epicranial  aponeurosis.  The  meshes  formed  by 
these   fibrous   processes  are  filled  with  small  lobules  of  fat, 


P§Mi§    Integument 

£_    Superficial  fascia 


B-    Kpicranial  aponeurosis 
Lax  connective  tissue 
Pericranium 

Cranial  wall 


Dura  mater 


Fig.  51. — Section  through  the  Scalp  and  Cranial  Wall. 

which  give  this  layer  a  granular  appearance.  As  the  fascia  is 
traced  forwards  towards  the  forehead,  and  downwards  on 
each  side  towards  the  ears,  it  loses  in  great  part  its  dense 
fibrous  character,  and  becomes  looser  and  less  fatty.  It  is  in 
the  superficial  fascia  that  the  cutaneous  vessels  and  nerves 
ramify  before  they  enter  the  skin. 

Dissection.- — The  superficial  fascia  may  now  be  removed  from  the  surface 
of  the  occipito-frontalis.  In  doing  this,  the  dissector  must  proceed  very 
cautiously,  so  as  not  to  injure  the  cutaneous  nerves  and  blood  vessels  which 
ramify  in  its  midst.  It  is  impossible,  owing  to  its  density,  to  raise  it  in 
one  layer  ;  it  must  be  taken  away  piecemeal. 

Occipito-frontalis  (epicranius).  —  This  is  a  (juadricipital 
muscle  which  presents  two  occipital  and  two  frontal  bellies. 
The  occipital  bellies  (musculi  occipitales) — Fig.  52  (2) — are 
quite  distinct  from  each  other,  and  are  separated  by  a  marked 
interval.      Each  arises  from  the  outer  twu-thirds  of  the  superior 


106  HEAD  AND  NECK 

curved  line  of  the  occipital  bone,  and  from  a  small  portion  of 
the  adjoining  part  of  the  mastoid  process  of  the  temporal 
bone  immediately  above  the  insertion  of  the  sterno-mastoid. 
From  this  the  fibres  ascend  for  a  distance  of  about  two  inches 
in  the  form  of  a  thin,  dark-red,  fleshy  layer,  which  is  inserted 
into  the  epicranial  aponeurosis. 

The  frontal  bellies  (musculi  frontales)  are  composed  of 
pale  fibres,  and  are  not  perfectly  distinct  from  each  other. 
For  a  short  distance  above  the  root  of  the  nose  their  inner 
margins  are  blended  along  the  middle  line.  Above  this, 
however,  they  diverge  slightly,  and  are  separated  by  a 
narrow  interval.  They  possess  little  or  no  direct  attach- 
ment to  the  bone.  The  greater  number  of  the  fibres 
mingle  with  those  of  the  orbicularis  palpebrarum  and  the 
corrugator  supercilii  muscles,  and  gain  an  attachment  to 
the  integument  and  subcutaneous  tissue  over  the  eyebrow, 
whilst  a  few  of  the  innermost  fibres  proceed  downwards 
upon  the  nasal  bone  to  form  the  pyramidalis  nasi  muscle. 
Ascending  upon  the  forehead,  the  frontal  bellies  are  inserted 
near  the  line  of  the  coronal  suture  into  the  epicranial 
aponeurosis. 

Epicranial  Aponeurosis  (galea  aponeurotica). — This  apo- 
neurosis connects  the  occipital  and  frontal  bellies  of  the 
occipito-frontalis  muscle,  and  constitutes  a  continuous  layer 
over  the  summit  and  sides  of  the  head.  Posteriorly  it  can 
be  traced  backwards  in  the  interval  between  the  two  occipital 
bellies  of  the  muscle,  when  it  will  be  observed  to  have  an 
attachment  to  the  external  occipital  protuberance  and  the 
superior  curved  line  of  the  occipital-  bone.  Laterally,  it 
presents  no  sharply  defined  margin,  but,  losing  its  aponeurotic 
character,  it  is  prolonged  downwards  as  a  fine  expansion  over 
the  temporal  fascia.  In  this  locality  it  gives  origin  to  two  of 
the  small  auricular  muscles. 

Dissection. — Divide  the  epicranial  aponeurosis  by  a  mesial  incision 
of  about  an  inch  and  a  half  in  length,  and  then  carry  across  the  middle 
of  this  a  second  short  transverse  cut.  On  raising  the  corners  thus 
marked  out,  the  aponeurosis  will  be  seen  to  rest  upon  a  layer  of  loose 
flocculent  areolar  tissue,  containing  no  fat — the  fourth  stratum  of  the 
scalp.  Owing  to  the  great  laxity  of  this  tissue,  the  occipito-frontalis 
muscle  by  its  contractions  can  move  the  hairy  scalp  freely  over  the 
pericranium  which  invests  the  bone. 

Extrinsic  Muscles  of  the  Ear. — In  man  these  muscles 
are    very    poorly    developed,    and    the    auricle    possesses    in 


SCALP  107 

consequence  only  a  very  limited  power  of  independent 
movement.      They  are  three  in  number,  viz.  : — 

1.  Attollens  auriculam. 

2.  Attrahens  auriculam. 

3.  Retrahens  auriculam. 

The  first  two  of  these  are  so  thin  that  it  requires  an  ex- 
perienced and  careful  dissector  to  isolate  them  from  the 
superficial  fascia. 

Attollens  auriculam  (musculus  auricularis  superior) — Fig. 
52  (1). — -To  expose  this  muscle  the  upper  part  of  the 
auricle  must  be  dragged  downwards,  and  then  fixed  in  this 
position  by  means  of  a  hook.  The  muscular  fibres  are  thus, 
rendered  tense  and  stand  out  in  relief.  When  cleaned  it 
will  be  seen  to  be  a  fan-shaped  muscle,  placed  immediately 
above  the  ear.  Above,  it  is  broad,  and  arises  from  the 
epicranial  aponeurosis  where  it  covers  the  temporal  fascia ; 
below,  the  fibres  converge  as  they  approach  the  auricle  and 
gain  an  insertion  into  the  upper  part  of  the  cranial  surface 
of  the  pinna. 

The  attrahens  auriculam  (musculus  auricularis  anterior), 
which  is  smaller  than  the  preceding,  is  placed  in  front  of 
the  ear,  and  the  auricle  must  therefore  be  pulled  backwards 
in  order  that  its  fibres  may  be  rendered  tense.  It  arises  on 
the  surface  of  the  temporal  fascia  from  the  epicranial  apo- 
neurosis, and  it  is  inserted  into  the  anterior  aspect  of  the 
helix  of'the  pinna. 

The  retrahens  auriculam  (musculus  auricularis  posterior) — 
Fig.  52  (3) — consists  of  two  or  three  short  bundles  of 
muscular  fibres  which  spring  from  the  mastoid  process  of 
the  temporal  bone,  and  are  inserted  into  the  posterior  part 
of  the  concha.  It  is  readily  exposed  by  drawing  the  ear 
forwards. 

The  attrahens  auriculam  is  supplied  by  a  twig  from  the 
temporal  branches  of  the  facial  nerve  ;  the  retrahe?is  and 
attollens  by  the  posterior  auricular  branch  of  the  facial 
nerve. 

Nerves  of  the  Scalp.  —  Two  nerves  are  given  to  the 
frontal  and  parietal  portions  of  the  scalp  by  the  frontal 
branch  of  the  ophthalmic  division  of  the  trigeminal  nerve. 
These  are  (a)  the  supra-trochlear,  (b)  the  supra-orbital. 

The  supra-trochlear  nerve  (nervus  supra-trochlearis)  leaves 
the  orbit   close  to  its  inner  angle  and   then   turns  upwards 


io8 


HEAD  AND   NECK 


Fig.  52. — Superficial  Nerves  on  the  Side  of  the  Neck  and  Back  of  the  Scalp. 
(Hirschfeld  and  Leveille\ ) 


1.  Attollens  auriculam. 

2.  Posterior  belly  of  occipito- 

frontalis. 

3.  Retrahens  auriculam. 

4.  Great  occipital  nerve. 

5.  Great  auricular  nerve. 

6.  Splenius  muscle. 

7.  Sterno-mastoid  muscle. 

8.  Small  occipital  nerve  (pre- 

sent as  two  branches). 


Great  auricular  nerve. 
External  jugular  vein. 
Superficial  cervical  nerve. 
Spinal  accessory  nerve. 
Descending    branches    of 

cervical  plexus. 
Cervical       branches        to 

trapezius 

15.  Trapezius  muscle. 

16.  Clavicular  branches. 


*3 


14 


'7 


Acromial  branches. 
Auricular    twigs    of  great 
auricular  nerve. 

19.  Parotid  gland. 

20.  Facial  nerve. 

21.  Masseter  muscle. 

22.  Infra-mandibular  nerve. 

23.  Anterior  jugular  vein. 

24.  Sternal  branches. 

25.  Platy.Nma  myoides. 


SCALP  109 

under  cover  of  the  orbicularis  palpebrarum.  It  becomes 
superficial  by  piercing  the  frontal  portion  of  the  occipito- 
frontalis,  and,  after  a  short  course  in  the  superficial  fascia, 
it  ends  in  the  integument  of  the  forehead. 

The  supra-orbital  nerve  (nervus  supra-orbitalis)  is  much 
larger  than  the  preceding,  and  quits  the  orbit  by  turning 
upwards  in  the  supra-orbital  notch.  The  position  of  this 
notch  in  the  superior  margin  of  the  orbit  can  generally  be 
detected  by  the  finger.  The  nerve  now  ascends  under 
cover  of  the  orbicularis  palpebrarum  and  the  frontal  belly 
of  the  occipito-frontalis,  and  divides  into  an  inner  and  an 
outer  division.  There  is  a  slight  difference  in  the  manner 
in  which  these  reach  the  surface.  The  inner  division 
becomes  superficial  by  piercing  the  anterior  belly  of  the 
occipito-frontalis,  whilst  the  outer  division  comes  to  the 
surface  a  little  farther  back  by  piercing  the  epicranial 
aponeurosis.  Both  ramify  in  the  superficial  fascia  over  the 
parietal  bone,  and  give  numerous  twigs  to  the  skin.  The 
outer  division  can  be  traced  as  far  back  as  the  lambdoidal 
suture. 

In  the  temporal  ?-egion,  nerves  from  three  sources  are  to 
be  found, — (a)  from  the  facial  nerve  ;  (b)  from  the  orbital 
branch  of  the  superior  maxillary  division  of  the  trigeminal 
nerve  ;  (c)  from  the  auriculo-temporal  branch  of  the  inferior 
maxillary  division  of  the  trigeminal  nerve. 

The  temporal  branches  of  the  facial  nerve  will  be  noticed 
running  upwards  over  the  zygoma.  They  furnish  twigs  of 
supply  to  the  attrahens  auriculam,  frontal  belly  of  the 
occipito-frontalis,  orbicularis  palpebrarum,  and  corrugator 
supercilii. 

The  temporal  branch  of  the  o?'bital  nerve  (ramus  zygo- 
maticotemporalis)  is  a  minute  twig,  which  is  somewhat 
difficult  to  find.  If  the  finger  be  carried  downwards  from 
the  external  angular  process  of  the  frontal  bone  along  the 
posterior  margin  of  the  malar  bone,  a  tubercle  on  the  latter 
will  be  felt.  This  is  the  guide  to  the  temporal  branch 
of  the  orbital  nerve;  it  pierces  the  temporal  fascia  im- 
mediately behind  it.  It  therefore  makes  its  appearance 
about  one  inch  above  the  anterior  part  of  the  zygoma,  and 
the  dissector  is  frequently  led  to  it  by  a  communicating 
twig  from  one  of  the  facial  branches.  It  is  distributed  to 
a  limited  area  of  skin  in  this  region. 


no  HEAD  AND  NECK 

The  auriculotemporal  nerve  (nervus  auriculotemporalis)  will 
be  found  immediately  in  front  of  the  ear,  in  close  contact 
with  the  superficial  temporal  artery.  It  soon  divides  into 
two  branches,  which  diverge  from  each  other  as  they  ascend, 
and  a  careful  dissector  may  be  able  to  trace  twigs  from  these 
as  far  as  the  summit  of  the  head.  Its  branches  terminate  in 
the  skin  of  the  scalp. 

In  the  mastoid  and  occipital  regions  of  the  scalp,  the  dissector 
will  meet  with  four  nerves,  each  from  a  different  source:  (a) 
the  posterior  auricular  branch  of  the  facial  nerve — Fig.  52 
(3)  I  ip)  tne  mastoid  branch  of  the  great  auricular  nerve ;  (c) 
the  small  occipital  nerve  from  the  anterior  primary  division 
of  the  second  cervical  nerve — Fig.  52  (8);  and  (d)  the 
great  occipital  nerve  from  the  posterior  primary  division  of 
the  second  cervical  nerve — Fig.  52  (4). 

The  posterior  auricular  (nervus  auricularis  posterior)  is  a 
small  nerve  which  ascends  upon  the  front  of  the  mastoid 
process,  immediately  behind  the  ear,  to  supply  the  superficial 
muscles  in  this  region.  The  guide  to  it  is  the  posterior 
auricular  artery,  which  lies  in  contact  with  it.  After  effecting 
a  communication  with  the  great  auricular  nerve,  it  divides 
into  an  auricular  and  an  occipital  division.  The  auricular 
division  continues  its  upward  course,  and  ends  by  supplying 
the  retrahens  auriculam  and  attollens  auriculam  muscles ;  the 
occipital  division  inclines  backwards  along  the  superior  curved 
line  of  the  occipital  bone,  and  ends  in  the  occipital  belly  of 
the  occipito-frontalis  muscle. 

In  searching  for  the  posterior  auricular  nerve,  the  dissector 
will,  in  all  probability,  meet  with  the  mastoid  branch  of  the 
great  auricular  nerve,  which  ascends  upon  the  mastoid  process 
on  a  more  superficial  plane,  and  is  distributed  to  the  skin  in 
this  region. 

The  small  occipital  nerve  (nervus  occipitalis  minor)  will  be 
discovered  midway  between  the  ear  and  the  external  occipital 
protuberance.  It  supplies  numerous  branches  to  the  integu- 
ment, and  furnishes  an  auricular  twig  to  the  skin  over  the 
upper  part  of  the  cranial  aspect  of  the  ear.  It  communicates 
with  the  great  auricular  nerve  on  the  one  hand,  and  with  the 
great  occipital  nerve  on  the  other. 

The  great  occipital  (nervus  occipitalis  major)  is  a  large 
nerve,  and  there  will  be  little  difficulty  experienced  in  finding 
it,   as  it   lies   close  to  the  occipital  artery,   a  short  distance 


SCALP  1 1 1 

external  to  the  occipital  protuberance.  Its  branches  spread 
out  over  the  back  of  the  head,  and  supply  a  wide  area  of 
integument.  It  sends  an  auricular  twig  to  the  skin  over  the 
cranial  aspect  of  the  ear,  and  communicates  with  the  small 
occipital  nerve. 

Blood  Vessels  of  the  Scalp. — Two  small  arteries,  viz.,  the 
frontal  and  the  supra-orbital,  both  branches  of  the  ophthalmic, 
leave  the  orbit  to  supply  the  forehead.  The  former  is  associ- 
ated with  the  supra-trochlear  nerve,  and  the  latter  with  the 
supra-orbital  nerve.  The  veins  corresponding  to  these  arteries 
unite  at  the  inner  margin  of  the  orbit  to  form  the  angular 
vein,  which  afterwards  becomes  the  facial  vein. 

The  superficial  temporal  artery  (arteria  temporalis  super- 
ficialis)  will  be  noticed  ascending  upon  the  temporal  fascia, 
immediately  in  front  of  the  ear.  At  a  variable  point  above 
the  zygoma  it  divides  into  its  two  terminal  branches — viz.,  the 
anterior  and  posterior  superficial  temporal  arteries. 

The  anterior  superficial  temporal  artery  (ramus  frontalis) 
takes  a  tortuous  course  upwards  and  forwards  to  the  forehead, 
and  supplies  numerous  branches  to  the  integument,  muscles, 
and  pericranium.  Further,  it  anastomoses  with  the  frontal 
and  supra-orbital  arteries,  and  with  the  corresponding  vessel 
of  the  opposite  side. 

The  posterior  superficial  tempoi-al  artery  (ramus  parietalis) 
inclines  upwards  and  backwards,  arching  over  the  cranium 
above  the  auricle.  It  gives  off  numerous  twigs  to  the  parts  in 
this  region,  and  communicates  with  its  fellow  of  the  opposite, 
side,  and  with  the  posterior  auricular  and  occipital  arteries. 

The  posterior  auricular  artery  (arteria  auricularis  posterior) 
ascends  in  the  angle  between  the  cartilage  of  the  ear  and  the 
mastoid  process,  and  ends  by  dividing  into  two  branches, 
named  respectively  the  auricular  and  the  mastoid.  The 
auricular  branch  ascends  under  cover  of  the  retrahens  auriculam 
muscle,  and  supplies  several  twigs  to  the  pinna,  and,  finally 
turning  forwards  above  the  auricle,  it  anastomoses  with  the 
posterior  superficial  temporal  artery.  The  mastoid  branch  in- 
clines backwards  towards  the  occiput,  where  it  communicates 
with  the  occipital  artery. 

The  posterior  auricular  vein  is  a  comparatively  large  vessel. 
It  joins  the  posterior  division  of  the  temporo-maxillary  vein, 
near  the  angle  of  the  lower  jaw,  to  form  the  external  jugular 
vein. 


ii2  HEAD  AND   NECK 

The  occipital  artery  (arteria  occipitalis),  which  will  be  found 
a  short  distance  to  the  outer  side  of  the  occipital  protuberance, 
sends  large  tortuous  branches  over  the  back  of  the  head. 
These  anastomose  with  the  corresponding  vessels  of  the 
opposite  side,  and  with  the  posterior  auricular  and  posterior 
temporal  arteries. 

Temporal  Fascia  (fascia  temporalis). — If  the  epicranial 
aponeurosis  with  the  attached  auricular  muscles  be  now  raised 
in  the  temporal  region,  a  thin  but  distinct  sheet  of  fascia  will 
be  observed  proceeding  from  the  upper  temporal  line  of  the 
parietal  bone,  in  close  relation  to  the  deep  surface  of  the 
attollens  auriculam,  to  the  pinna.  When  this  is  removed  the 
strong  temporal  fascia  which  covers  the  temporal  muscle  is 
brought  fully  into  view.  Its  connections  will  be  studied  at  a 
later  period. 

Surgical  Anatomy  of  the  Scalp. — The  close  connexion  between  the 
three  superficial  layers  of  the  scalp  (viz.,  skin,  superficial  fascia,  and  epi- 
cranial aponeurosis),  and  the  loose  manner  in  which  these  are  bound  by 
areolar  tissue  to  the  pericranium,  are  points  of  great  interest  from  a  surgical 
point  of  view.  When  the  scalp  is  wrenched  from  the  head  by  machinery, 
or  by  any  other  means,  the  separation  is  effected  in  the  plane  of  the  areolar 
layer.  The  blood  vessels,  however,  lie  for  the  most  part  in  the  superficial 
fascia,  and  therefore  large  flaps  of  detached  scalp  can  be  replaced  upon  the 
denuded  periosteum,  and  yet  retain  their  vitality.  It  is  a  rare  occurrence 
for  a  scalp  flap  to  slough. 

The  scalp  is  richly  supplied  with  blood  vessels.  Incised  wounds  in  this 
region,  therefore,  bleed  very  profusely  ;  but,  in  addition  to  this,  they  bleed 
with  more  than  usual  persistence.  This  is  accounted  for  by  the  dense 
character  of  the  superficial  fascia,  and  by  the  fact  that  the  fibrous  septa  of 
this  stratum  adhere  to  the  coats  of  the  vessels,  and  prevent  them  from 
retracting  freely  when  divided. 

As  will  readily  be  understood,  a  collection  of  pus  in  the  scalp  will  pro- 
duce very  different  results,  according  to  the  position  it  occupies.  If  it  is 
formed  under  the  epicranial  aponeurosis  it  spreads  in  all  directions ; 
indeed,  it  is  only  limited  in  front  by  the  superciliary  ridges  of  the  frontal 
bone,  and  behind  by  the  superior  curved  line  of  the  occipital  bone.  If  it 
is  formed  in  the  superficial  fascia,  it  is  confined  to  the  point  at  which  it 
originates. 


REMOVAL  OF  THE   BRAIN. 

On  the  second  day  after  the  subject  has  been  placed  on 
the  table,  the  two  dissectors  of  the  head  and  neck  should,  in 
conjunction  with  each  other,  proceed  to  remove  the  brain. 

Dissection. — The  head  being  supported  upon  a  block,  an  incision  is 
made  along  the  middle  line  of  the  head,  through  the  epicranium,  the  sub- 
jacent areolar  tissue,  and  the  pericranium,  from  the  root  of  the  nose  in 


REMOVAL  OF  THE  BRAIN 


113 


front,  to  the  external  occipital  protuberance  behind.  This  must  be  done 
boldly,  so  as  to  divide  everything  right  down  to  the  bone.  With  a  series 
of  sharp  strokes  with  the  handle  of  the  scalpel,  the  pericranium  on  each 
side  can  easily  be  turned  outwards,  so  as  to  leave  the  bone  perfectly  bare. 
Observe,  however,  that  although  the  pericranium  is  loosely  attached  over 
the  surface  of  the  various  bones  of  the  vault,  it  is  firmly  attached  along 
the  lines  of  the  cranial  sutures  by  processes  that  dip  in  between  the  bones, 
so  as  to  separate  their  edges.  On  reaching  the  temporal  ridges,  push  the 
knife  through  the  attachment  of  the  temporal  fascia,  so  that  the  blade  lies 
between  the  temporal  muscle  and  the  bone.  Then  run  the  knife  back- 
wards and  forwards,  so  as  to  thoroughly  divide  the  attachment  of  the  fascia 
to  the  ridge.  When  this  is  done  on  either  side,  the  fascia  and  muscle  can 
be  easily  raised  together  from  the  temporal  fossa,  and  thrown  down  over 
the  ear  with  the  remains  of  the  scalp. 


Vein 


Sub-arachnoid  space  and  trabeculae 


--  Dura  mater 
-  -Subdural  space 
"-Arachnoid  mater 
N  Pia  mater 


Fig.  53. — Diagrammatic  section  through  the  Meninges  of 
the  Brain.      (Schwalbe. ) 

co.  Grey  matter  of  cerebral  convolutions. 

The  dissectors  should  next  obtain  a  saw,  a  chisel,  and  a  mallet,  and 
proceed  to  remove  the  calvaria.  The  line  along  which  the  saw  is  to  be 
used  may  be  marked  out  on  the  skull  by  encircling  it  with  a  piece  of  string, 
and  then  marking  the  cranium  with  a  pencil  along  the  line  of  the  string. 
In  front,  the  cut  should  be  made  fully  three-quarters  of  an  inch  above  the 
margins  of  the  orbits  ;  behind,  it  should  be  carried  round  at  the  level  of  a 
point  midway  between  the  lambda1  and  the  external  occipital  protuberance. 
The  saw  should  only  be  used  to  divide  the  outer  table  of  the  skull.  When 
the  diploe  is  reached,  which  will  be  observed  by  the  sawdust  becoming  red 
and  moist,  the  saw  should  be  abandoned.  The  hammer  and  chisel  are 
now  brought  into  requisition,  and  by  these  the  inner  table  can  readily  be 
split  along  the  line  in  which  the  outer  table  of  the  cranium  is  divided.  By 
insinuating  the  hook  at  the  end  of  the  cross-bar  of  the  chisel  into  the  fissure 
in  front,  the  skull-cap  can  be  forcibly  wrenched  off. 


1  The  term  "  lambda  "  signifies  the  apex  of  the  occipital  bone,  or  the  point 
at  which  the  sagittal  and  lambdoidal  sutures  meet. 

VOL.  II — 8 


ii4  HEAD   AND  NECK 

Dura  Mater  (dura  mater  encephali). — The  brain  is  clothed 
by  three  distinct  membranes,  which  are  termed  the  meninges. 
These  are  from  without  inwards  —  (i)  the  dura  mater;  (2) 
the  arachnoid  mater;  and  (3)  the  pia  mater. 

When  the  skull-cap  is  detached,  the  outer  surface  of  the 
dura  mater,  as  it  covers  the  upper  surface  of  the  cerebral 
hemispheres,  is  exposed.  It  is  rough,  and  dotted  over  with 
bleeding  points.  If  a  portion  were  placed  in  water,  its  rough- 
ness would  become  still  more  manifest,  and  be  seen  to  be 
due  to  a  multitude  of  fine  fibrous  and  vascular  processes,  by 
which  it  is  connected  with  the  deep  surface  of  the  bones. 
These  have  necessarily  been  torn  asunder  in  the  removal  of 
the  skull-cap.  The  bleeding  points  are  most  numerous  along 
the  middle  line,  or,  in  other  words,  along  the  line  of  the 
superior  longitudinal  sinus ;  and  if  the  handle  of  the  knife  be 
run  from  before  backwards,  so  as  to  make  pressure  along  this 
line,  a  considerable  quantity  of  blood  will  ooze  out.  This 
shows  that  a  number  of  small  veins  from  the  cranial  bones 
have  been  ruptured.  The  degree  of  adhesion  between  the 
dura  mater  and  the  inner  surface  of  the  cranial  bones  varies 
in  different  subjects  and  in  different  localities.  In  all  cases 
it  is  strongly  adherent  along  the  lines  of  the  sutures ;  and, 
further,  it  is  much  more  firmly  attached  to  the  base  than  the 
vault  of  the  cranium.  In  the  child — indeed,  as  long  as  the 
bones  of  the  cranium  are  growing — it  is  more  adherent  than 
in  the  adult ;  and  it  is  also  more  firmly  bound  to  the  bone  in 
old  age. 

The  dissector  should  now  clean  the  outer  surface  of  the 
dura  mater  with  a  sponge.  He  will  then  recognise  the  middle 
meningeal  artery  upon  each  side,  ascending  in  the  substance 
of  the  membrane,  and  sending  off  its  branches  in  a  widely 
arborescent  manner.  It  stands  out  in  bold  relief  from  the 
membrane  in  which  it  ramifies  ;  and  if  the  skull-cap  be 
examined,  its  inner  surface  will  be  observed  to  be  deeply 
grooved  by  its  ramifications.  The  meningeal  arteries,  as  the 
name  might  lead  one  to  imagine,  are  not  intended  for  the 
supply  of  the  membrane  alone.  They  must  also  be  looked 
upon  as  the  nutrient  vessels  of  the  inner  table  and  diploe  of 
the  cranial  bones. 

The  Pacchionian  bodies  (granulationes  arachnoidales),  which 
are  almost  invariably  present,  and  which  are  as  a  rule  best 
marked  in  old  subjects,  will  attract  notice  at  this  stage.     They 


REMOVAL  OF  THE  BRAIN 


US 


are  small  granular  bodies,  ranged  in  clusters  on  either  side  of 
the  superior  longitudinal  sinus,  into  which  many  of  them 
protrude  (Fig.  54).  As  a  general  rule,  they  are  most  evident 
towards  the  hinder  part  of  the  parietal  region.  At  first  sight 
these  bodies  appear  to  be  protrusions  from  the  dura  mater, 
but  this  is  not  the  case.  They  spring  from  the  arachnoid 
mater,  and  are  enlargements  of  the  normal  villi  of  this 
membrane. 

The  relation  which  the  Pacchionian  bodies  present  to  the  dura  mater 
is  somewhat  intricate.  When  they  project  into  the  superior  longitudinal 
sinus  they  push  before  them  a  thin  covering  continuous  with  the  floor  of 
the  sinus,  so  that  in  no  sense  can  they  be  said  to  pierce  its  wall.  On  either 
side  of  the  superior  longitudinal   sinus   there  are  a  number  of  irregular 


Pacchionian  body 


Opening  of  cerebral  vein 


Bone 


FiG.  54. — Mesial  section  through  the  Frontal  Bone  and  corresponding  part  of 
the  Longitudinal  Blood  Sinus.  The  Pacchionian  bodies  are  seen  pro- 
truding into  the  sinus.      (Enlarged.) 

spaces  or  intervals  which  communicate  with  the  sinus  either  by  a  small 
aperture  or  a  narrow  channel.  These  recesses  are  termed  parasinoidal 
sinuses  or  lacnnce  laterales,  and  the  independent  meningeal  veins,  and  some 
of  the  diploic  veins,  pour  their  blood  into  them.  Pacchionian  bodies  push 
themselves  into  the  parasinoidal  sinuses  from  below  in  such  a  manner  that 
they  receive  a  complete  covering  by  the  invagination  of  the  floor.  Nor  does 
the  bone  escape.  As  the  Pacchionian  bodies  enlarge,  they  cause  absorption 
of  the  cranial  wall,  and  small  pits  are  hollowed  out  on  its  deep  surface  for 
their  reception.  The  superficial  walls  of  the  lacunre — very  much  thinned 
— line  these  depressions  in  the  calvaria. 

Two  Layers  of  the  Dura  Mater. — Having  learned  these 
preliminary  details  from  an  examination  of  the  outer  surface 
of  the  dura  mater,  as  it  clothes  the  upper  surface  of  the 
rebral  hemispheres,  the  student  is  in  a  position  to  under- 
stand that  this  membrane  does  not  belong  entirely  to  the 
brain.  It  performs  a  double  function:  (1)  it  acts  as  an 
internal  periosteum  to  the  bones  forming  the  cranial  cavity  ; 
11— 8  a 


u6 


HEAD  AND  NECK 


and  (2)  it  gives  support  to  the  different  parts  of  the  brain. 
Consequently,  it  consists  of  two  strata,  which,  in  most  localities, 
are  firmly  adherent,  but  which  nevertheless  can  usually  be 
easily  demonstrated  in  the  dissecting-room.  These  strata 
may  very  appropriately  be  termed  the  endocranial  and  the 
supporting  layers.  Along  certain  lines  these  two  layers  separate 
from  each  other.  In  some  cases  they  separate  so  as  to  form 
channels,  termed  blood  sinuses  (sinus  durae  matris),  for  the 
conveyance  of  venous  blood  ;  in  other  cases  they  separate  in 


Parasinoidal  sinus 
Pacchionian  ^^^^(j^g^^^^^ 


'CA 


Pacchionian  body 
Parasinoidal  sinus 


Longitudinal  sinus 


Blood  vessels-' 

Grey  cortex  of  a 

convolution 


Dura  mater 


Pia  mater 
Subarachnoid  space 


Falx  cerebri 


Fig.  55. — Diagram  of  a  coronal  section  through  the  middle  portion  of  the 
cranial  vault  and  subjacent  brain  to  show  the  membranes  of  the  brain 
and  the  Pacchionian  bodies. 

order  that  the  inner  supporting  layer  may  form  strong  folds 
or  partitions,  which  run  in  between  the  various  parts  of  the 
brain.  By  these  latter  the  cranial  cavity  is  divided  into  com- 
partments communicating  freely  with  each  other,  and  each 
holding  a  definite  subdivision  of  the  brain  (Fig.  57). 

Dissection. — These  points  must  now  be  verified.  Begin  by  tilting  the 
head  forwards.  Support  it  in  this  position,  and  make  two  incisions  through 
the  dura  mater  in  an  antero-posterior  direction-one  on  each  side  of  the 
superior  longitudinal  sinus,  and  along  its  whole  length.  From  the  mid- 
point of  each  of  these  incisions  another  cut  must  be  made  through  each 
lateral  portion  of  the  dura  mater  downwards  to  the  cut  margin  of  the  skull 
immediately  above  the  ear  (Fig.  56).  The  dura  mater  covering  the  upper 
aspect  of  the  brain  is  thus  divided  into  a  central  strip  containing  the 
superior  longitudinal  sinus  and  four  triangular  flaps.  The  flaps  should 
now  be  turned  downwards  over  the  cut  margin  of  the  skull,  and  in  this 


REMOVAL  OF  THE  BRAIX 


ii7 


position  they  preserve  the  brain  during  its  removal  from  laceration  by  the 
sharp  bony  edge. 

Subdural    Space    (cavum    subdurale). — This    is    the    term 
which  is  applied  to  the  interval  between  the  dura  mater  and 


the  arachnoid  mater- 


-Figs. 


53   and   55.      It  contains  a  very 


small  quantity  of  serous  fluid  which  moistens  the  opposed 
surfaces  of  these   membranes.     A  striking  contrast  between 


superior 

longitudinal 

sinus 

Pacchionian 

bodies 

Middle 

meningeal 

artery 


Mouth  of 
cerebral  vein 
Cerebral 

vein 


Fig.  56. — The  Dura  Mater  and  the  Superior  Longitudinal 
Sinus,  etc.  The  lines  along  which  the  dura  mater  should 
be  incised  in  removing  the  brain  are  indicated  by  dotted 
lines  on  the  right  side. 

the  two  surfaces  of  the  dura  mater  will  be  observed.  The 
superficial  surface,  as  we  have  noted,  is  rough  and  flocculent. 
The  deep  surface,  which  is  turned  towards  the  subdural  space, 
is  smooth,  polished,  and  glistening. 

The  cerebral  veins  returning  the  blood  from  the  surface  of 
the  cerebral  hemispheres  will  be  seen  shining  through  the 
arachnoid.  They  are  lodged  for  the  most  part  in  the  sulci 
between  the  convolutions,  and  run  upwards  to  the  middle 
line.  Reaching  the  superior  longitudinal  sinus  they  are 
suddenly  directed  forwards,  and  lie  against  the  wall  of  the 
sinus  for  some  distance  before  they  open  into  it  (Fig.  56). 
n 


n8 


HEAD  AND  NECK 


Superior  Longitudinal  Sinus  (sinus  sagittalis  superior). — 
Open  into  this  venous  channel  by  running  the  knife  through 
its  upper  wall  from  behind  forwards  (Figs.  56  and  57).  It 
begins  in  front  at  the  crista  galli  of  the  ethmoid  bone,  where 
it  not  unfrequently  communicates  with  the  veins  in  the 
nasal  cavity  through  the  foramen  caecum,  and  it  extends 
backwards,   grooving  the  cranial  vault  in  the  middle  line,  to 

Falx  cerebri 

Inferior  longitudinal  sinus 
Superior  longitudinal 


Cavernous  sinus 


Eustachian 
tube 

Nasal 
septum 


Vena  Galeni  magna 


Tentorium 


Straight 
sinus 


Lateral  sinus 

Falx  cerebelli 
Lateral  sinus 
Inferior  petrosal  sinus     Superior  petrosal  sinus 

Fig.  57. — Sagittal  section  through  the  Skull  a  little  to  the  left  of  the 
mesial  plane  to  show  the  processes  of  Dura  Mater. 


V.   Fifth  cranial  nerve. 
VII.   Facial  nerve. 
VIII.  Auditory  nerve. 


IX.  Glossopharyngeal  nerve. 

X.  Vagus  nerve. 
XL  Spinal  accessory  nerve. 
XII.    Hypoglossal  nerve. 


the  internal  occipital  protuberance,  on  the  right  aspect  ot 
which  it  becomes  continuous  with  the  right  lateral  sinus. 
Its  lumen,  which  is  triangular  in  cross-section,  is  very  small 
in  front,  but  expands  greatly  as  it  is  followed  backwards. 
The  mouths  of  the  superior  cerebral  veins  are  observed 
opening  into  it.  These  veins  pour  their  blood  into  it 
in  a  direction  contrary  to  that  in  which  the  blood  flows 
within  the  channel.  The  terminal  portions  of  the  veins  are 
directed  from  behind  forwards,  whilst  the  blood  in  the  sinus 
flows  from  before  backwards.      Opening  into  the  sinus  are  also 


REMOVAL  OF  THE  BRAIN  119 

the  mouths  of  the  lacuna  laterales,  whilst  bulging  into  it  on 
either  side  are  as  a  rule  numerous  Pacchionian  bodies.  The 
channel  is  crossed  at  its  inferior  angle  by  a  number  of  minute 
bands.     These  receive  the  name  of  chorda  Willisii. 

Falx  Cerebri  (Fig.  57). — This  is  a  sickle-shaped  redupli- 
cation of  the  supporting  layer  of  the  dura  mater,  which 
descends  in  the  mesial  plane  between  the  two  cerebral 
hemispheres.  In  order  to  expose  it,  the  cerebral  veins,  as 
they  open  into  the  superior  longitudinal  sinus,  must  be 
divided,  and  the  hemisphere  gently  pulled  outwards.  In 
front,  the  falx  cerebri  is  narrow,  and  attached  to  the  crista 
galli  of  the  ethmoid  bone.  As  it  is  followed  backwards,  it 
increases  in  breadth,  and  behind,  it  is  attached  in  the  middle 
line  to  the  upper  surface  of  the  tentorium  cerebelli.  The 
anterior  part  of  the  falx  is  frequently  cribriform,  and  is  some- 
times perforated  by  apertures  to  such  an  extent  that  it 
almost  resembles  lace-work.  Along  each  border  it  splits  into 
two  layers  so  as  to  enclose  a  blood-sinus.  Along  its  upper 
convex  margin  runs  the  superior  longitudinal  sinus ;  along  its 
concave  free  border  courses  the  much  smaller  inferior  longi- 
tudinal sinus ;  whilst  along  its  attachment  to  the  tentorium  is 
enclosed  the  straight  sinus.  Its  inferior  concave  margin 
overhangs  the  corpus  callosum,  with  which,  however,  it  is  not 
in  contact,  except,  perhaps,  to  a  very  slight  extent,  behind. 

Removal  of  the  Brain. — The  dissectors  should  now 
proceed  to  remove  the  brain.  Having  divided  the  attach- 
ment of  the  falx  cerebri  to  the  crista  galli,  pull  it  backwards. 
Next,  removing  the  block  upon  which  the  head  rests,  and 
supporting  the  occiput  and  posterior  lobes  of  the  brain  with 
the  left  hand,  let  the  head  drop  well  backwards.  In  all 
probability,  the  frontal  lobes  will  fall  away  by  their  own 
weight  from  the  anterior  fossa  of  the  base  of  the  cranium, 
and  perhaps  carry  with  them  the  olfactory  bulbs.  Should 
they  remain  in  position,  however,  gently  raise  them  with  the 
lingers,  and  separate,  at  the  same  time,  with  the  handle  of 
the  knife  the  olfactory  bulbs  from  the  cribriform  plate  of  the 
ethmoid.  In  raising  the  olfactory  bulbs,  the  minute  olfactory 
nerves  which  spring  from  them  and  perforate  the  cribriform 
plate  of  the  ethmoid  bone  are  torn  across.  The  large  round 
and  white  optic  nerves  (second  pair  of  cranial  nerves)  now 
come  into  view  as  they  leave  the  cranium  through  the  optic 
foramina.  When  these  are  divided,  the  internal  carotid  arteries 
ii— 8  c 


i2o  HEAD  AND  NECK 

will  be  exposed,  and  between  them,  in  the  mesial  plane,  the 
infundibulum,  a  hollow  conical  process  which  connects  the 
pituitary  body  with  the  tuber  cinereum — a  lamina  of  grey 
matter  on  the  base  of  the  brain.  It  will  be  noticed  that  the 
infundibulum  lies  slightly  behind  the  internal  carotid  arteries.1 
Sever  in  turn  each  of  these  structures.  We  then  come  upon 
the  oculo-7)iotor  ?ierves  (third  pair  of  cranial  nerves),  which 
must  be  dealt  with  in  like  manner.  Observe  first,  however, 
that  they  lie  behind,  and  external  to  the  carotid  trunks. 
The  dissector  should  now  see  upon  either  side  the  anterior 
extremity  of  the  inner  free  margin  of  the  tentorium  cerebelli 
as  it  passes  forward  to  be  attached  to  the  anterior  clinoid 
process.  Pressing  this  outwards  with  the  point  of  the  knife, 
the  minute  trochlear  nerve  (fourth  cranial  nerve)  will  be 
brought  into  view.  It  lies  under  shelter  of  the  free  border  of 
the  tentorium,  and  should  be  divided  at  this  stage.  The 
head  must  in  the  next  place  be  turned  forcibly  round,  so 
that  the  face  is  directed  over  the  left  shoulder.  On  raising 
the  posterior  part  of  the  right  cerebral  hemisphere  with  the 
fingers,  it  will  be  observed  to  rest  upon  the  tentorium  cere- 
belli— a  broad  horizontal  process  of  dura  mater,  which  inter- 
venes between  it  and  the  cerebellum.  Divide  the  tentorium 
along  its  attached  border,  and  take  care  in  doing  this  not 
to  injure  the  subjacent  cerebellum.  When  the  division  is 
effected,  push  the  tentorium  backwards  out  of  the  way  with 
the  point  of  the  knife.  Now  turn  the  head  so  as  to  bring 
its  left  side  uppermost,  and  treat  the  tentorium  on  this  side 
in  the  same  manner.  The  two  parts  of  the  trigeminal  nerve 
(fifth  cranial  nerve)  perforating  the  dura  mater  near  the  apex 
of  the  petrous  portion  of  the  temporal  bone ;  the  abducent 
nerve  (sixth  cranial  nerve)  piercing  the  dura  mater  behind  the 
dorsum  sellse  of  the  sphenoid  bone ;  the  portio  dura  or  facial 
nerve,  the  pars  intermedia,  and  the  portio  mollis  or  auditory 
nerve  disappearing  into  the  internal  auditory  meatus ;  the 
glossopharyngeal,  the  vagus,  and  the  spinal  accessory  nerves 
leaving  the  skull  through  the  jugular  foramen ;  and  the  two 
slips  of  the  hypoglossal  nerve  piercing  the  dura  mater  over  the 
anterior  condyloid  foramen,  will  each  in  turn  come  into  view 
upon  either  side,  and  each  must  be  divided  in  succession. 

1  In  dividing  the  cranial  nerves,  it  is  well  to  cut  them  close  to  the  point 
where  they  pierce  the  dura  mater  on  one  side  of  the  body,  and  close  to  the 
brain  on  the  other  side. 


REMOVAL  OF  THE  BRAIN  121 

In  the  case  of  the  three  nerves  passing  out  of  the  cranium 
through  the  jugular  foramen,  the  dissector  should  endeavour 
to  leave  the  spinal  accessory  of  the  right  side  intact  within 
the  cranium,  by  dividing  its  roots  of  origin  from  the  medulla, 
whilst  on  the  other  side  he  should  remove  it  with  the  brain. 
This  nerve  will  be  readily  recognised  from  its  ascending  from 
the  spinal  canal  into  the  cranial  cavity  through  the  foramen 
magnum.  It  is  only  necessary  now  for  the  dissector  to  thrust 
the  knife  into  the  spinal  canal,  and  divide  the  vertebral 
arteries  as  they  turn  forwards  upon  the  upper  part  of  the 
spinal  cord,  and  then  sever  at  a  lower  level  the  spinal  cord, 
the  spinal  accessory  nerve  of  the  left  side,  and  the  roots  of 
the  first  pair  of  spinal  nerves.  By  letting  the  head  fall  well 
backwards,  and  gently  dislodging  the  medulla  and  cerebellum, 
the  whole  brain  can  be  removed.  The  veins  of  Galen,  as 
they  pass  from  the  interior  of  the  brain  to  enter  the  straight 
sinus,  are  ruptured  by  this  proceeding. 

Preservation  of  the  Brain. — In  order  that  the  brain  may  be  studied  to 
best  advantage,  it  is  necessary  that  it  should  be  subjected  to  some  harden- 
ing reagent.  Methylated  spirit,  with  a  small  amount  of  formalin  (4  per 
cent)  added  to  it,  gives  the  best  results.  The  dissector  must  obtain  a 
vessel  large  enough  to  hold  the  brain,  and,  at  the  same  time,  allow  the 
hardening  reagent  to  surround  and  cover  it  completely.  It  must  likewise 
be  provided  with  an  accurately  fitting  lid  to  prevent  evaporation.  A 
small  amount  of  cotton  wadding  should  be  arranged  at  the  bottom  of  the 
vessel,  in  the  form  of  a  nest,  so  as  to  preserve,  as  far  as  possible,  the 
natural  form  of  the  brain.  The  brain  should  be  placed  upon  this,  with 
its  base  or  lower  surface  uppermost,  and  the  meninges  of  the  base  should 
be  torn  across,  so  as  to  give  free  admission  to  the  fluid.  It  is  well  also 
to  raise  the  cerebellum  slightly  from  the  cerebrum  by  means  of  a  small 
pad  of  wadding,  and  it  is  advantageous  to  tear  across  the  arachnoid  at  the 
back  of  the  corpus  callosum. 

It  is  best  to  defer  the  study  of  the  brain  until  the  dissection  of  the 
head  and  neck  is  completed. 

Dura  Mater  at  the  Base  of  the  Cranium. — The  dissector 
has  observed  that  the  dura  mater  can,  as  a  rule,  be  easily 
separated  from  the  under  surface  of  the  cranial  vault.  He 
would  find  it  impossible  to  raise  it  in  like  manner  from  the 
base  of  the  cranium.  It  is  closely  adherent  to  the  crista 
galli,  to  the  posterior  margins  of  the  lesser  wings  of  the 
sphenoid,  to  the  posterior  clinoid  processes,  to  the  petrous 
portions  of  the  temporal  bones,  to  the  basilar  process  of  the 
occipital  bone,  and  around  the  margin  of  the  foramen 
magnum.  Another  cause  of  its  close  adhesion  in  this 
locality  is,   that  it  gives  sheaths   to  the  cranial    nerves,   and 


122  HEAD  AND  NECK 

passes  out  of  the  cranium  through  the  basal  foramina  to 
become  continuous  with  the  periosteum  on  the  external 
surface  of  the  skull.  So  close,  indeed,  is  the  union  between 
the  dura  mater  and  the  base  of  the  cranium,  that  it  would 
require  maceration  to  effect  a  complete  separation. 

Partitions  of  Dura  Mater. — The  dura  mater  gives  off,  as 
we  have  already  seen,  processes  which  act  as  partial  partitions 
within  the  cranial  cavity.     These  are  four  in  number,  viz. : — 

i.  The  falx  cerebri  (which  has  already  been  studied). 

2.  The  tentorium  cerebelli. 

3.  The  falx  cerebelli. 

4.  The  diaphragma  sellse. 

Tentorium  Cerebelli  (Fig.  57  and  Fig.  58).  —  This  is 
a  large  crescentic  fold  of  dura  mater  which  constitutes  a 
membranous  roof  for  the  posterior  fossa  of  the  cranium,  and 
at  the  same  time  forms  a  partition  between  the  posterior 
lobes  of  the  cerebrum  and  the  cerebellum.  It  is  not  hori- 
zontal. It  is  accurately  applied  to  the  upper  surface  of  the 
cerebellum.  Its  highest  point,  therefore,  is  in  front,  in  the 
mesial  plane,  and  from  this  it  gradually  slopes  downwards  to 
its  attached  border.  Except  in  cases  where  formalin  has 
been  injected  into  the  cranial  cavity  during  the  preservation 
of  the  subject,  only  an  imperfect  idea  of  the  natural  appear- 
ance of  the  tentorium  can  be  obtained,  seeing  that  its 
connections  have  been  severed  in  the  removal  of  the  brain. 
Before  it  is  disturbed  it  is  tense,  and  this  tension  is  due  to 
its  connection  with  the  falx  cerebri.  These  two  processes 
of  dura  mater  are  mutually  dependent  on  each  other  in  this 
respect — divide  one,  and  both  become  relaxed. 

The  posterior  border  of  the  tentorium  is  convex,  and  is 
attached  to  the  horizontal  ridge  which  marks  the  deep  surface 
of  the  occipital  bone.  Beyond  this,  on  each  side,  it  is  fixed 
to  the  posterior  inferior  angle  of  the  parietal  bone,  and  then 
forwards  along  the  upper  border  of  the  petrous  portion  of 
the  temporal  bone.  From  the  internal  occipital  protuber- 
ance to  the  postero-inferior  angle  of  the  parietal  bone  this 
border  encloses  the  lateral  blood  sinus,  whilst  along  the  upper 
border  of  the  petrous  bone  it  encloses  the  superior  petrosal 
sinus.  The  anterior  border  of  the  tentorium  is  sharp,  free,  and 
concave,  and  forms,  with  the  dorsum  sellae  of  the  sphenoid,  an 
oval  opening  (incisura  tentorii),  within  which  the  mesencephalon 
is  placed.     Beyond  the  apex  of  the  petrous  portion  of  the  tern- 


REMOVAL  OF  THE  BRAIN 


123 


poral  bone  the  two  margins  of  the  tentorium  cross  each 
other  like  the  limbs  of  the  letter  X  ;  the  free  margin  is  carried 
forwards  to  be  attached  to  the  anterior  clinoid  process,  whilst 
the  attached  border  is  continued  inwards  to  be  fixed  to  the 
posterior  clinoid  process  (Fig.  59). 

Falx  Cerebelli. — This  is  a  small  falciform  fold  of  dura  mater 
placed  under  the  tentorium,  which  extends  forwards  in  the 
mesial  plane  from  the  internal  occipital  crest  (Fig.  58).  It 
occupies  the  notch  which  separates  the  two  lateral  hemispheres 


Cerebral 
fossa' 


Superior  longitudinal  sinus 


cerebri 


Tentorium 


Tentorium 
cerebelli 


Fig.  58. — Coronal  section  through  the  Cranial  Cavity  in  a  plane  which 
passes  through  the  hinder  part  of  the  foramen  magnum.  The 
posterior  part  of  the  cranial  cavity,  from  which  the  brain  has  been 
removed,  is  depicted. 

of  the  cerebellum  posteriorly.  Above,  it  is  attached  to  the 
posterior  part  of  the  under  surface  of  the  tentorium.  Its 
anterior  border  is  free  ;  whilst  inferiorly,  it  bifurcates  into  two 
small  diverging  ridges,  which  gradually  fade  away  as  they  are 
traced  forwards  on  either  side  of  the  foramen  magnum. 

Diaphragma  Sellae. — This  is  a  small  circular  fold  of  the 
inner  layer  of  the  dura  mater  which  forms  a  roof  for  the  sella 
turcica.  A  small  opening  is  left  in  its  centre  for  the  passage 
of  the  infundibulum.  An  almost  complete  case  of  dura  mater 
is  thus  formed  for  the  pituitary  body. 

Cranial  Nerves. — The  dissector  should  now  turn  his  atten- 
tion to  the  cranial  nerves,  and  study  the  manner  in  which 


124 


HEAD  AND  NECK 


they  leave  the  cranial  cavity.  Each  nerve  carries  out  with  it 
a  covering  derived  from  each  of  the  three  membranes  of  the 
brain.  In  the  case  of  the  optic  nerve  these  remain  distinct ; 
but  in  all  the  others  the  sheath  derived  from  the  arachnoid 
very  soon  disappears. 

Begin  by  examining  the  cribriform  plate  of  the  ethmoid. 
From  this  the  olfactory  bulb  has  been  displaced  in  the  removal 
of  the  brain.  About  twenty  minute  olfactory  nerves  (nervi 
olfactorii)  proceed  from  the  under  surface  of  the  bulb  and 
descend  into  the  nose  through  the  holes  in  the  cribriform 
plate.  These  have  been  ruptured  close  to  their  origin,  but 
in  all  probability  traces  of  them  will  be  observed. 


Optic  nerve 


Olivary  process  of  sphenoid 
Optic  foramen 


Oculo-motor 

cranial  nerve 

Trochlear  cranial  nerve 

Trigeminal  cranial  nerve 


Hypoglossal  nerve— - 


Anterior  clinoid  process 
Posterior  clinoid  process 


jr- Abducent  cranial  nerve 

Anterior  free  edge 
of  tentorium 
The  aperture  in  front 
of  the  tentorium 


FlG.  59. — Aperture  between  the  Dorsum  Sella;  and  the  anterior  concave 
free  margin  of  the  Tentorium.      (Hirschfeld  and  Leveille. ) 

The  second  or  optic  nerve  (nervus  opticus) — Figs.  59  and  60 
— will  be  seen  entering  the  orbit  through  the  optic  foramen. 
It  is  accompanied  by  the  ophthalmic  artery,  which  lies  below 
it.  The  student  should  note  the  strong  loose  sheath  of  dura 
mater  which  envelops  the  nerve. 

The  third  or  oculo-motor  nerve  (nervus  oculomotorius) — 
Figs.  59  and  60 — is  a  firm  cord-like  nerve,  which  pierces 
the  dura  mater  in  front  of  the  posterior  clinoid  process,  within 
a  triangular  area  indistinctly  marked  out  by  the  intersection 
of  the  margins  of  the  tentorium,  as  they  pass  to  be  attached 
to  the  clinoid  processes.  The  nerve  enters  the  wall  of  the 
cavernous  sinus,  in  which  it  will  be  afterwards  traced. 


REMOVAL  OF  THE1  BRAIN 


125 


The  minute  thread-like  fourth  or  trochlear  nerve  (nervus 
trochlearis) — Figs.  59  and  60 — also  enters  the  wall  of  the 
cavernous  sinus,  to  gain  which  it  perforates  the  dura  mater 
a  short  distance  behind,  and  to  the  outer  side  of  the  third 
nerve,  but  within  the  same  triangular  area.  Its  aperture  of 
exit  lies  under  shelter  of  the  free  margin  of  the  tentorium. 


Infundibulum 

.Sixth  nerve 

Fifth  nerve 

Fourth  nerve^    JM 

Auditory  and 
facial  nerves 

Glosso-pharyn- 

geal  nerve"~  jf* 

Vagus  nerve— Jjfii 


Hypoglossal 

nerve    i 
Spinal  accessory    \j^ 
nerve 

Section  through  \ 
the  medulla 


Lateral 


Optic  nerve 

Internal  carotid 
artery 

i\ 

.     Posterior 
%r^communicating 

,  Vj  -Third  nerve 

Jii_Posterior  cerebral 
f^|\_Superior 
cerebellar 


Tentorium 

Basilar 
artery 

Vertebral 
artery 

Superior  petrosal 

sinus 


Lateral  sinus 


;ipital  sinus 


Superior  longitudinal  sinus 


Straight  sinus  divided 


FlG.  60.  —  Floor  of  the  Cranium  after  the  removal  of  the  Brain  and  the 
Tentorium  Cerebelli.  'I  lie  blood  vessels  forming  the  circle  of  Willis 
have  been  left  in  place. 

The  fifth  or  trigeminal  nerve  (nervus  trigeminus) — Figs.  59 
and  60 — is  composed  of  two  parts — viz.,  a  large,  soft,  sensory 
portion,  consisting  of  loosely  connected  funiculi,  and  a  small, 
firmer,  motor  portion,  which  lies  upon  the  inner  or  deep 
surface  of  the  sensory  part.  They  can  generally  be  easily 
distinguished,  and  both  pierce  the  dura  mater  at  the  apex  of 
the  petrous  portion  of  the  temporal  bone,  and  under  the 
anterior  extremity  of  the  tentorium. 


126  HEAD  AND   NECK 

The  sixth  or  abducent  nerve  (nervus  abducens) — Figs.  59 
and  60 — is  a  small,  round  nerve,  which  disappears  through 
the  dura  mater  at  the  lower  and  outer  part  of  the  dorsum 
sellae,  and  enters  the  wall  of  the  cavernous  sinus. 

The  auditory  7ierve  (nervus  acusticus),  the  facial  nerve 
(nervus  facialis)  (Fig.  60),  and  the  small  pars  intermedia 
(nervus  intermedius),  all  enter  the  auditory  meatus,  where 
the  pars  intermedia  joins  the  facial  nerve.  They  are  accom- 
panied by  the  auditory  artery. 

The  glosso- pharyngeal  (nervus  glossopharyngeus),  the  pneumo- 
gastric  (nervus  vagus),  and  the  spinal  accessory  (nervus  acces- 
sorius)  pierce  the  dura  mater  over  the  internal  jugular  foramen 
in  the  order  in  which  they  have  been  named,  from  before 
backwards  (Fig.  60).  The  glosso-pharyngeal  has  a  separate 
aperture  of  exit  in  the  dura  mater,  and  therefore  receives  a 
separate  sheath  of  dura  mater,  whilst  the  vagus  and  spinal  acces- 
sory have  a  common  aperture,  and  a  common  sheath  of  both 
arachnoid  and  dura  mater.  They  all  leave  the  skull  through  the 
middle  compartment  of  the  jugular  foramen.  The  spinal  acces- 
sory has  already  been  noticed  ascending  from  the  spinal  canal. 

The  hypoglossal  nerve  (nervus  hypoglossus)  pierces  the  dura 
mater  opposite  the  anterior  condyloid  foramen  at  two  separate 
points,  in  the  form  of  two  distinct  slips  (Fig.  60).  These 
unite  in  the  foramen. 

Venous  Blood  Sinuses  (sinus  durae  matris). — The  blood 
sinuses  which  traverse  the  dura  mater  should  next  be  ex- 
amined. Each  should  be  opened  in  turn  by  running  the 
knife  through  the  dura  mater  which  forms  its  wall.  The 
following  is  a  list  of  these  sinuses  : — 

1.  Superior  longitudinal.  6.  Spheno-parietal. 

2.  Inferior  longitudinal.  7.  Circular. 

3.  Straight.  8.  Superior  petrosal. 

4.  Occipital.  9.  Inferior  petrosal. 

5.  Cavernous.  10.  Basilar. 

11.   Lateral. 

As  already  pointed  out,  the  cranial  blood  sinuses  are  in 
some  cases  formed  by  a  separation  of  the  two  layers  of  the 
dura  mater ;  in  other  cases  they  are  formed  in  the  reduplica- 
tions of  the  inner  layer  of  the  dura  mater  which  constitute 
the  partitions.  The  channels  thus  constituted  are  lined  by 
a  smooth  membrane,  which  is  continuous  with  the  internal 
coat  of  the  veins. 


REMOVAL  OF  THE  BRAIN  127 

Torcular  Herophili  (confluens  sinuum). — The  superior  longi- 
tudinal sinus  has  been  already  examined,  except  at  the  point 
where  it  terminates.  The  dissector  should  notice  that  as  it 
descends  upon  the  deep  surface  of  the  occipital  bone,  it,  as 
a  rule,  inclines  slightly  to  one  or  other  side  of  the  mesial 
plane,  more  usually  to  the  right  side,  and  in  this  way  it 
terminates  upon  one  side  of  the  internal  occipital  protuber- 
ance. Here  it  is  somewhat  dilated,  and  then  turns  suddenly 
outwards,  to  form  the  lateral  sinus  of  that  side.  This  ex- 
pansion of  the  superior  longitudinal  sinus  is  termed  the 
torcular  Herophili,  and  it  communicates  by  means  of  a  trans- 
verse channel,  which  crosses  the  front  of  the  internal  occipital 
protuberance,  with  the  commencement  of  the  lateral  sinus  of 
the  opposite  side. 

Inferior  Longitudinal  Sinus  (sinus  sagittalis  inferior) — 
Fig.  57. — This  small  sinus  runs  backwards  in  the  lower 
free  border  of  the  falx  cerebri.  It  begins  at  a  variable  point 
behind  the  crista  galli,  and  ends  posteriorly  at  the  anterior 
free  edge  of  the  tentorium,  where  it  pours  its  blood  into  the 
straight  sinus. 

Straight  Sinus  (sinus  rectus). — This  venous  channel  ex- 
tends backwards  and  downwards  in  the  mesial  plane,  from 
the  anterior  free  edge  of  the  tentorium  to  the  internal  occipital 
protuberance.  Its  course  corresponds  with  the  attachment 
of  the  posterior  broad  end  of  the  falx  cerebri  to  the  upper 
surface  of  the  tentorium.  Indeed,  it  is  formed  by  the  opening 
out  of  the  two  layers  of  the  falx  on  the  upper  surface  of  the 
tentorium.  At  its  anterior  extremity  it  receives  the  blood 
from  the  inferior  longitudinal  sinus  and  the  vena  magna 
Galeni.  The  latter  returns  the  blood  from  the  interior  of  the 
cerebrum,  and  its  ruptured  end  may  be  noticed  at  the  point 
where  it  enters  the  straight  sinus  (Fig.  57).  At  the  internal 
occipital  protuberance,  the  straight  sinus  bends  suddenly 
outwards,  in  a  direction  opposite  to  that  taken  by  the  superior 
longitudinal  sinus,  and  it  forms  the  lateral  sinus  of  that  side. 
A  few  small  cerebellar  veins  pour  their  blood  into  the  straight 
sinus. 

Occipital  Sinus  (sinus  occipitalis)  —  Fig.  60. — This  is  a 
minute  blood-channel,  which  is  placed  between  the  layers  of 
the  falx  cerebelli.  Above,  it  opens  into  the  torcular  Herophili, 
whilst  below,  at  the  foramen  magnum,  it  bifurcates,  and  the 
two  divisions  not  infrequently  run   forwards  to  join  the  lower 


i28  HEAD  AND   NECK 

end  of  the  lateral  sinus  upon  either  side.  Sometimes  the 
occipital  sinus  is  double  throughout  its  whole  course. 

Lateral  Sinuses  (sinus  transversi) — Figs.  57  and  58. — These 
are  two  in  number — one  on  each  side.  They  are  variable  in 
their  mode  of  origin,  but,  as  we  have  noted,  the  right  lateral 
sinus  is  commonly  formed  by  the  superior  longitudinal  sinus, 
whilst  the  left  is  formed  by  the  straight  sinus.  They  com- 
mence one  upon  either  side  of  the  internal  occipital  protuber- 
ance, and  communicate  with  each  other  by  a  transverse 
channel  of  variable  width,  which  passes  in  front  of  this  bony 
prominence.  The  sinus  which  represents  the  continuation  of 
the  superior  longitudinal  sinus  is  generally  considerably  larger 
than  the  other.  From  the  occipital  protuberance,  each  lateral 
sinus  passes  at  first  outwards  and  upwards,  and  grooves  the 
occipital  bone  and  the  inferior  angle  of  the  parietal  bone 
along  the  attached  border  of  the  tentorium.  Reaching  the 
temporal  bone,  it  is  joined  by  the  superior  petrosal  sinus ; 
and  leaving  the  tentorium,  it  suddenly  curves  downwards  and 
inwards,  in  the  deep  furrow  upon  the  mastoid  portion  of  the 
temporal  bone,  and  the  jugular  process  of  the  occipital  bone. 
Lastly,  it  turns  forwards  and  disappears  into  the  posterior 
compartment  of  the  jugular  foramen,  where  it  terminates 
in  the  bulb  of  the  internal  jugular  vein.  In  this  course 
the  lateral  sinus  describes  an  arch  (Birmingham)  with  the 
convexity  upwards,  the  highest  point  of  which,  as  a  rule, 
corresponds  with  the  posterior  inferior  angle  of  the  parietal 
bone. 

Venous  tributaries  which  come  from  the  cerebellum,  back 
part  of  the  cerebrum,  and  from  the  diploe  of  the  cranial 
bones,  may  be  noticed  opening  into  the  lateral  sinus. 

Two  large  and  important  emissary  veins  connect  it  with 
the  veins  of  the  scalp,  and  allow  its  blood,  when  it  is  over- 
charged, to  drain  partly  away  in  this  direction.  These  are 
the  mastoidal  vein  (emissarium  mastoideum),  joining  it  through 
the  mastoid  foramen,  and  the  posterior  co?idyloid  vein  (emis- 
sarium condyloideum),  which  joins  it  through  the  posterior 
condyloid  foramen. 

Cavernous  Sinus  (sinus  cavemosus) — Fig.  57. — It  is  not 
advisable  that  the  dissector  should  open  the  cavernous  sinus 
at  this  stage,  on  account  of  the  various  nerves  which  pass 
forwards  in  its  walls  to  the  orbit,  and  which  are  best  studied 
with  the  parts  in  that  cavity.      He  should  simply  note,  there- 


REMOVAL  OF  THE  BRAIN  129 

fore,  at  present,  that  this  sinus  lies  upon  the  side  of  the  body 
of  the  sphenoid  bone. 

Circular  Sinus  (sinus  circularis).  —  The  circular  sinus 
is  formed  of  two  transverse  channels  (the  anterior  and  the 
posterior  intercavernous  sinuses)  which  connect  the  cavernous 
sinuses,  and  lie  one  in  front  and  the  other  behind  the  infundi- 
bulum  of  the  pituitary  body. 

Petrosal  Sinuses — Fig.  57. — The  petrosal  sinuses  drain 
the  blood  from  the  posterior  end  of  the  cavernous  sinus. 
They  are  two  in  number  on  each  side — viz.,  superior  and 
inferior.  The  superior  petrosal  sinus  (sinus  petrosus  superior) 
runs  along  the  superior  border  of  the  petrous  portion  of  the 
temporal  bone,  and  joins  the  lateral  sinus.  The  inferior 
petrosal  sinus  (sinus  petrosus  inferior)  is  the  larger  of  the  two, 
but  has  a  shorter  course.  It  passes  backwards  and  outwards 
in  the  groove  between  the  basilar  process  of  the  occipital 
bone  and  the  inferior  margin  of  the  petrous  portion  of  the 
temporal  bone.  It  leaves  the  cranial  cavity  by  passing 
through  the  anterior  compartment  of  the  jugular  foramen, 
and  ends  by  joining  the  commencement  of  the  internal 
jugular  vein. 

Basilar  Sinus  (plexus  basilaris).  —  The  basilar  sinus  is 
not  a  single  channel,  but  a  plexus  of  minute  sinuses  which 
permeate  the  dura  mater  over  the  basilar  process  of  the 
occipital  bone.  It  connects  the  two  inferior  petrosal  sinuses, 
and  communicates  below  with  the  anterior  intraspinal  veins. 

Spheno-Parietal  Sinus  (sinus  alae  parvae). — The  spheno- 
parietal sinus  is  a  minute  blood  channel  which  runs  in- 
wards on  each  side  under  shelter  of  the  lesser  wing  of 
the  sphenoid  bone.  Externally  it  commences  in  one  of  the 
meningeal  veins,  whilst  internally  it  pours  its  blood  into  the 
fore-part  of  the  cavernous  sinus.  Owing  to  its  position,  this 
sinus  is  somewhat  difficult  to  demonstrate. 

Petro  Squamous  Sinus. — Very  frequently  a  small  blood  channel  will 
be  noticed  running  backwards  along  the  petro-squamous  fissure,  in  the 
angle  between  the  squamous  and  petrous  parts  of  the  temporal  bone.  It 
is  of  importance  in  connection  with  the  surgery  of  the  middle  ear. 

Arteries  entering  the  Cranial  Cavity. — The  student  has 
now  examined  the  various  channels  by  means  of  which  the 
venous  blood  is  drained  out  of  the  cranial  cavity.  He  should 
next  examine  the  arteries  which  introduce  the  blood  into  this 
cavity.     These  are — 

VOL.  11  —  9 


130  HEAD  AND  NECK 

1.  The  vertebral  arteries. 

2.  The  internal  carotid  arteries. 

3.  The  meningeal  arteries. 

Vertebral  and  Internal  Carotid  Arteries. — These  vessels 
carry  blood  for  the  supply  of  the  encephalon  and  the  parts 
within  the  orbit.  The  i?tternal  carotid  artery  will  be  observed 
piercing  the  dura  mater  immediately  behind,  and  to  the 
inner  side  of  the  anterior  clinoid  process.  At  this  point  it 
gives  off  its  ophthalmic  branch  which  accompanies  the  optic 
nerve  through  the  optic  foramen,  and  immediately  beyond 
this  the  internal  carotid  trunk  has  been  severed  in  the 
removal  of  the  brain.  The  vertebral  artery  will  be  observed 
piercing  the  dura  mater  immediately  below  the  foramen 
magnum,  through  which  it  enters  the  cranium.  Here  it 
passes  between  the  highest  denticulation  of  the  ligamentum 
denticulatum  and  the  hypoglossal  nerve.  It  also  has  been 
divided  close  to  its  point  of  entrance. 

Meningeal  Arteries. — These  are  the  nutrient  arteries  of 
the  dura  mater,  and  the  inner  table  and  diploe  of  the  cranial 
bones.  They  are  derived  from  a  great  number  of  different 
sources,  but  the  only  one  of  any  size  is  the  middle  meningeal, 
which  comes  from  the  internal  maxillary  artery.  The  others 
are  small  twigs,  and,  except  in  a  well-injected  subject,  will 
not  be  easily  made  out.  They  are: — (1)  anterior  meningeal 
from  the  anterior  ethmoidal  artery;  (2)  the  small  meningeal 
from  the  internal  maxillary  artery;  (3)  some  small  branches  from 
the  ascending  pharyngeal,  occipital,  and  vertebral  arteries. 

The  middle  meningeal  artery  (arteria  meningea  media),  a 
branch  of  the  internal  maxillary  artery,  enters  the  cranium 
through  the  foramen  spinosum  of  the  sphenoid,  and  divides 
upon  the  deep  surface  of  the  great  wing  of  that  bone  into 
two  large  terminal  branches.  Of  these,  the  anterior  branch 
ascends  upon  the  great  wing  of  the  sphenoid,  and  the  anterior 
inferior  angle  of  the  parietal  bone,  grooving  both  deeply, 
whilst  the  posterior  branch  turns  backwards  upon  the 
squamous  portion  of  the  temporal  bone.  The  branches 
which  proceed  from  these  trunks  spread  out  widely  and 
occupy  the  arborescent  grooves  on  the  deep  surface  of  the 
cranial  vault. 

Two  veins  accompany  the  middle  meningeal  artery.  They 
pass  through  the  foramen  spinosum  and  unite  in  a  common 
trunk  which  joins  the  pterygoid  plexus. 


REMOVAL  OF  THE  BRAIN 


T31 


The  anterior  meningeal  artery  (arteria  meningea  anterior) 
proceeds  from  the  anterior  ethmoidal  artery  as  it  lies  on  the 
cribriform  plate  of  the  ethmoid  bone,  along  with  the  nasal 
nerve.  It  supplies  a  limited  area  of  dura  mater  and  bone  in 
the  anterior  fossa  of  the  cranium. 

The  small  meningeal  artery  (ramus  meningeus  accessorius) 
is  somewhat  inconstant,  and  not  infrequently  springs  from 
the  middle  meningeal.  It  enters  the  cranium  through  the 
foramen  ovale,  but  it  should  not  be  looked  for  at  the  present 
stage,  as  it  is  best  examined  along  with  the  Gasserian 
ganglion  and  the  three  divisions  of  the  trigeminal  nerve. 

The  meningeal  branches  from  the  ascending  pharyngeal  artery 


Fig.  6i. — i,  Pituitary  body;   2,  in  mesial  section  ; 
3,  in  horizontal  section.      (Schwalbe. ) 


a.  Anterior  lobe. 

b.  Posterior  lobe. 

cm.  Corpus  mammillare. 

i.  Tuber  cinereum. 

ch.  Optic  commissure  in  section. 


ro.   Optic  recess  of  the  third  ventricle. 
o.  Optic  nerve. 
a'.   Infundibulum  with  projection  from 

anterior    lobe    upwards   in    front 

of  it. 


are  the  terminal  twigs  of  this  vessel,  and  enter  the  cranium 
through  the  foramen  lacerum  medium,  through  the  jugular 
foramen,  and  through  the  anterior  condyloid  foramen.  The 
branch  which  passes  through  the  jugular  foramen  is  the 
largest. 

The  meningeal  branches  of  the  occipital  and  vertebral  arteries 
are  small.  The  former  enters  through  the  jugular  foramen, 
whilst  the  latter  gains  admittance  to  the  cranium  through  the 
foramen  magnum,  and  is  distributed  in  the  posterior  cranial 
fossa. 

The  meningeal  veins  may  be  regarded  as  being  arranged  in 
two  sets  :  one  set  consists  of  small  channels  which  pour  their 
blood  into  the  blood  sinuses;  the  other  set  is  composed  of 
small   veins    which    accompany   the    meningeal    arteries   and 


132  HEAD  AND  NECK 

carry  their  blood   to   venous  trunks  on    the  exterior  of  the 
cranium. 

Pituitary  Body  (hypophysis  cerebri) — Fig.  61. — The  over- 
hanging margin  of  the  diaphragma  sellas  should  be  freely  cut 
in  two  or  three  places,  and  the  pituitary  body  carefully  dis- 
lodged from  the  sella  turcica  of  the  sphenoid  bone.  If  this 
be  done  successfully,  the  body  will  be  seen  to  be  an  oval 
structure,  slightly  flattened  from  above  downwards,  and  with 
its  long  axis  directed  transversely.  Further,  it  may  be  noticed 
to  consist  of  a  large  anterior  lobe,  and  a  smaller  posterior 
lobe.  The  former  of  these  is  hollowed  out  behind  so  as  to 
form  a  concavity  for  the  lodgment  of  the  latter.  If  a  vertical 
section  be  made  through  the  bod)7,  the  line  of  separation 
between  the  two  lobes  is  very  distinct.  The  infundibulum 
which  connects  the  pituitary  body  with  the  tuber  cinereum 
of  the  brain  is  continued  into  the  posterior  lobe,  and  is  in 
no  way  structurally  continuous  with  the  larger  anterior  lobe, 
although  a  surface  inspection  of  the  body  is  apt  to  give  the 
dissector  that  impression  (Fig.  61,  i).  Thus,  even*  in  the 
adult,  we  have  a  clue  to  the  different  modes  of  development 
of  the  two  lobes.  The  posterior  lobe  is  derived  from  the  brain, 
whilst  the  anterior  lobe  is  an  offshoot  from  the  primitive 
buccal  cavity. 

The  dissectors  of  the  head  and  neck  must  now  prepare  for  the  changing 
of  the  position  of  the  subject.  Some  tow,  or  a  sponge,  soaked  in  a  mixture 
of  methylated  spirit  and  carbolic  acid  (to  which  a  little  formalin  may  be 
added  with  advantage),  should  be  introduced  into  the  cranial  cavity.  The 
skull-cap  should  then  be  replaced  and  retained  in  position  by  bringing  the 
scalp  flaps  over  it,  and  stitching  them  accurately  together.  It  is  a  common 
practice  with  students,  when  the  scalp  has  been  dissected  and  the  brain 
removed,  to  throw  the  skull-cap  aside.  This  proceeding  cannot  be  too 
strongly  condemned,  because  the  contour  of  the  head  is  then  lost,  and  in 
the  subsequent  dissection  false  conceptions  are  apt  to  be  formed. 


DORSAL  ASPECT  OF  THE  TRUNK. 

On  the  third  day  after  the  subject  has  been  placed  in  the 
dissecting-room  its  position  is  changed.  It  is  now  laid  on  its 
face,  with  its  chest  and  pelvis  supported  by  blocks.  The 
head  should  be  allowed  to  fall  well  over  the  end  of  the  table 
(Fig.  62).  During  the  four  days  that  the  body  is  allowed  to 
lie  in  this  position,  the  dissectors  of  the  head  and  neck  have 


DORSAL  ASPECT  OF  THE  TRUNK 


133 


to  dissect  the  dorsal  aspect  of  the  cervical,  thoracic,  lumbar, 
and  sacral  regions,  and,  in  addition,  remove  the  spinal  cord. 

The  dissectors  of  the  upper  limbs  take  part  in  this  dissection.  It  is 
their  duty  to  dissect  the  superficial  and  deep  fascice  in  the  thoracic  and 
lumbar  regions,  and  also  those  structures  which  connect  the  limb  to  the 
trunk  posteriorly.  To  them,  therefore,  belong  the  trapezius  muscle  below 
the  seventh  cervical  spine,  the  latissimus  dorsi  and  the  rhomboid  muscles, 
together  with  their  vessels  and  nerves  of  supply.  The  levator  anguli 
scapulae  and  the  omo-hyoid  are  to  be  regarded  as  common  property.  The 
dissectors  of  the  upper  limbs  are  allowed  two  days  to  complete  this  work. 

During  the  first  two  days  allowed  for  the  dissection  of 
the  back,  the  dissector  of  the  head  and  neck  has  merely  to 
examine  the  superficial  parts  on  the  back  of  the  neck,  and 


Fig.  62. 

take'part  along  with  the  dissector  of  the  upper  limb  in  the 
dissection  of  those  structures  which  are  common  to  both. 

The  first  day  should  be  devoted  to  the  reflection  of  the 
skin,  and  the  dissection  of  the  superficial  nerves  and  that 
portion  of  the  posterior  triangle  of  the  neck  which  can  be 
examined  in  the  present  position  of  the  subject.  On  the 
second  day  the  trapezius  may  be  reflected,  and  the  following 
structures  examined — viz.,  the  levator  anguli  scapulae  and  its 
nerves,  the  posterior  scapular  artery,  the  superficial  cervical 
artery,  the  suprascapular  artery  and  nerve,  the  transversalis 
colli  artery,  and  the  origin  of  the  omo-hyoid. 

Surface  Anatomy.  —  First  make  out  the  position  of  the 
external  occipital  protuberance,  and  having  traced  the  superior 
curved  line  of  the  occipital  bone  as  it  passes  outwards  towards 
the  mastoid  process,  press  deeply  into  the  neck  immediately 
below  the  occiput,   and  in   the  middle  line  ;    here  the   bifid 


i34  HEAD  AND  NECK 

extremity  of  the  massive  spinous  process  of  the  axis  vertebra 
can  be  felt.  In  the  middle  line  of  the  neck  is  the  nuchal 
furrow.  Carrying  the  finger  downwards  in  this,  the  posterior 
edge  of  the  ligamentum  nuchae  can  be  distinguished,  but  the 
short  spines  of  the  third,  fourth,  and  fifth  cervical  vertebrae 
as  a  rule  can  hardly  be  detected.  The  spines  of  the  sixth 
and  seventh  cervical  vertebrae,  however,  are  usually  very 
prominent. 

Reflection  of  Skin  (Fig.  62). — Three  incisions  are  required — (1)  Along 
the  middle  line,  from  the  external  occipital  protuberance  to  the  prominent 
spine  of  the  seventh  cervical  vertebra.  (2)  From  the  lower  end  of  this 
mesial  incision  transversely  outwards  to  the  inner  border  of  the  acromion 
process  of  the  scapula.  (3)  From  the  upper  end  of  the  primary  incision 
transversely  outwards  over  the  occiput  to  the  ear. 

The  quadrilateral  flap  of  skin  thus  marked  out  must  be  raised  from  the 
subjacent  superficial  fascia.  On  reaching  the  side  of  the  neck,  the  head 
must  be  held  well  over  to  the  opposite  side.  Here,  unless  the  dissector 
keep  close  to  the  skin,  there  is  a  danger  of  the  knife  slipping  in  under  the 
posterior  border  of  the  sterno-mastoid  muscle. 

Superficial  Nerves. — The  nerves  to  be  looked  for  in  the 

superficial  fascia,  which  is   now  exposed,   are  derived  partly 

from    the    posterior    primary  divisions,   and  partly  from    the 

anterior    primary    divisions    of   the    cervical    nerves.       They 

are  : — 

.  (   1,   Great  occipital. 

*rom  posterior       j    2    Terminal  twi  s  of  the  internal  branches 
primary  divisions.       (^  of  the  ^  fourthj  and  fifth  nerves 

From  anterior  f   1.   Small  occipital, 

primary  divisions.       ^  2-   Great  auricular. 

Dissection. — The  main  trunk  of  the  great  occipital  nerve  may  be  found 
piercing  the  trapezius  muscle  about  an  inch  below  the  occipital  protuber- 
ance, and  about  half  an  inch  external  to  the  m-esial  plane.  The  fascia  at 
this  spot  is  usually  very  dense,  and  the  readiest  method  to  adopt  in  ex- 
posing the  nerve  is  to  carefully  shave  it  off  in  slices  until  the  plane  of  the 
muscle  is  reached. 

The  great  occipital  (nervus  occipitalis  magnus)  —  Fig.  63 — 
is  the  internal  branch  of  the  posterior  primary  division  of 
the  second  cervical  nerve,  and  its  branches  of  distribution 
have  already  been  noticed,  spreading  out  on  the  back  of 
the  scalp  (p.  no).  As  it  becomes  superficial,  it  joins  the 
occipital  artery,  and  both  are  directed  upwards  to  supply 
the  scalp. 

The  terminal  twigs  of  the  internal  branches  of  tJie  posterior 
divisions  of  the  third,  fourth,  and  fifth  cervical  nerves  enter  the 


DORSAL  ASPECT  OF  THE  TRUNK 


i35 


superficial  fascia  close   to  the  mesial   plane,   and   then    turn 
transversely  outwards  to  supply  the  skin  of  the  neck. 

The  third  cervical  branch  sends  in  addition  a  large  twig 
upwards  to  the  integument  over  the  occiput.  This  nerve  runs 
along  the  inner  side  of  the  great  occipital,   and,   as  a  rule, 


Epicranial 
aponeurosis 

Great  occipital 
nerve 


Occipital  artery 


Posterior  hell}-  of 
occipi  to-frontal  is 


Complexus 

Retrahens 
aariculani 

Splenius  capitis 

Posterior 
auricular  nerve 

—      Parotid  gland 
Small  occipital  nerve 
Sterno-inastoid 
Great  auricular  nerve 

Levator  anguli  scapula; 


Kk;.  63. — Superficial  dissection  of  the  Back  of  the  Neck. 

communicates  with  it.      From  its  distribution,  it  is  frequently 
termed  the  third  occipital  nerve  (nervus  occipitalis  tertius). 

Dissection.   -The  small  occipital  nerve  will  be  found   by  dividing  the 
fascia  along  the  posterior  border  of  the  sterno-mastoid  muscle. 

The  small  occipital  nerve  (nervus  occipitalis  minor) — Fig. 
63 — springs  from  the  anterior  primary  division  of  the  second 
cervical  nerve,  and  runs  upwards  to  assist  in  the  supply  of  the 
integument  over  the  occiput.  Its  terminal  twigs  have  already 
been  dissected  in  the  superficial  fascia  of  the  scalp  (p.  110). 
11— 9  a 


136  HEAD  AND  NECK 

Occasionally  the  small  occipital  is  represented  by  two  separate 
nerves. 

Dissection. — The  great  auricular  nerve  can  readily  be  exposed  by  drawing 
the  head  well  over  to  the  opposite  side  and  then  dividing  the  fascia  over 
the  outer  surface  of  the  sterno-mastoid  muscle  very  obliquely.  Begin  the 
incision  at  the  posterior  margin  of  the  muscle  about  the  middle  of  the  neck, 
and  carry  it  upwards  and  forwards  towards  the  lobule  of  the  ear. 

The  great  auricular  ?ierve  (nervus  auricularis  magnus) — 
Fig.  63 — is  a  branch  of  the  cervical  plexus,  and  takes  origin 
from  the  second  and  third  cervical  nerves.  Turning  round 
the  posterior  border  of  the  sterno-mastoid  muscle,  it  proceeds 
upwards  and  forwards  on  the  surface  of  that  muscle  towards 
the  lobule  of  the  ear.  Near  this  point  it  will  be  found  to 
end  by  dividing  into  three  sets  of  branches — viz.,  facial, 
auricular,  and  mastoid. 

The  facial branches  will  be  traced  afterwards  in  the  dissection 
of  the  face.  The  others  may  be  followed,  however,  at  the 
present  stage.  The  auricular  branches  supply  the  integument 
upon  the  cranial  aspect  of  the  auricle  ;  and  if  they  be  carefully 
dissected,  several  of  them  will  be  noticed  to  pierce  the  cartilage 
to  reach  the  integument  on  its  outer  surface.  Communications 
may  also  be  made  out  between  these  twigs  and  the  posterior 
auricular  branch  of  the  facial  nerve.  The  mastoid  branch 
extends  upwards  upon  the  mastoid  process,  wrhere  it  is 
connected  with  the  posterior  auricular  and  small  occipital 
nerves. 

Dissection.—  Whilst  the  subject  is  lying  upon  its  face  we  can  only  obtain 
a  very  meagre  idea  of  the  posterior  triangle  of  the  neck.  It  is  only  its 
upper  and  least  important  part  which  can  at  present  be  exposed.  To  bring 
the  boundaries,  floor,  and  contents  of  this  portion  into  view,  the  dissector 
should  begin  by  cleaning  the  cervical  part  of  the  trapezius.  Occupying  the 
interval  between  the  trapezius  and  sterno-mastoid,  two  contiguous  muscles, 
taking  a  somewhat  oblique  course,  will  be  observed.  The  higher  of  these 
is  the  splenius  capitis,  and  the  lower  is  the  levator  anguli  scapulae.  These, 
together  with  the  posterior  border  of  the  sterno-mastoid,  must  be  cleaned. 
In  carrying  out  this  dissection  the  dissector  must  proceed  with  some  degree 
of  caution  ;  and  above  all,  he  must  be  careful  not  to  raise  the  sterno-mastoid 
nor  disturb  the  cervical  nerves  which  lie  under  cover  of  it,  because  these 
can  be  studied  at  much  greater  advantage  when  the  subject  is  turned.  In 
cleaning  the  levator  anguli  scapulae  the  dissector  must  secure  two  small 
nerves  which  issue  from  the  cervical  plexus  for  the  supply  of  that  muscle. 
They  are  closely  applied  to  its  surface,  and  are  apt  to  be  removed  with  the 
fascia  covering  the  muscle,  unless  they  are  specially  looked  for.  Further, 
the  spinal  accessory  nerve,  and  two  or  three  cervical  nerves  crossing  from 
the  posterior  border  of  the  sterno-mastoid  to  the  trapezius,  should  be 
dissected  out. 


DORSAL  ASPECT  OF  THE  TRUNK  137 

Posterior  Triangle. — The  upper  part  of  the  posterior 
triangle  which  is  thus  displayed  is  bounded  in  front  by  the 
posterior  border  of  the  sterno- mastoid,  and  behind  by  the 
anterior  border  of  the  trapezius.  The  apex,  which  is  directed 
upwards,  is  formed  at  the  superior  curved  line  of  the  occipital 
bone  by  the  apposition  of  the  occipital  attachments  of  these 
two  muscles.  The  floor  of  that  portion  of  the  space  which  is 
exposed  will  be  observed  to  be  formed  by  the  splenius  capitis 
and  the  levator  anguli  scapulae.  But  it  often  happens  that 
the  occipital  attachments  of  the  sterno-mastoid  and  trapezius 
(more  especially  of  the  latter)  are  so  poorly  developed  that 
they  fail  to  meet  on  the  superior  curved  line  of  the  occipital 
bone.  In  this  case  a  small  portion  of  the  complexus  (readily 
recognised  by  the  vertical  direction  of  its  fibres)  will  be 
noticed  entering  into  the  formation  of  the  floor  of  the  space 
above  the  level  of  the  splenius.  The  contents  of  the  space,  in 
so  far  as  they  can  be  seen  in  the  present  position  of  the  body, 
are — (1)  the  great  auricular  and  small  occipital  nerves  as  they 
appear  at  the  posterior  margin  of  the  sterno-mastoid  muscle ; 
(2)  the  spinal  accessory  nerve,  the  cervical  nerves  to  the 
trapezius,  and  two  small  nerves  from  the  cervical  plexus  to 
the  levator  anguli  scapulae.  An  additional  structure  also 
enters  the  space  when  the  sterno-mastoid  and  trapezius  do 
not  meet  to  form  a  distinct  apex  for  the  triangle,  viz.,  the 
occipital  artery.  In  such  a  case  a  small  portion  of  the  vessel 
will  be  noticed  upon  the  complexus  muscle,  close  to  the 
superior  curved  line  of  the  occipital  bone. 

Spinal  Accessory  Nerve  (nervus  accessorius). — This  im- 
portant nerve  appears  in  the  posterior  triangle  by  emerging 
from  the  substance  of  the  sterno-mastoid  muscle.  It  crosses 
the  triangle  obliquely,  running  from  above  downwards  and 
backwards,  and  finally  disappears  under  the  anterior  border  of 
the  trapezius. 

Cervical  Branches  to  the  Trapezius. — These  are  two  or 
three  nerves  which  spring  from  the  third  and  fourth  cervical 
trunks.  They  enter  the  posterior  triangle  by  leaving  the  shelter 
of  the  sterno-mastoid,  and  are  carried  downwards  and  back- 
wards across  the  space  parallel  with,  but  at  a  lower  level 
than,  the  spinal  accessory  nerve.  This,  together  with  the 
fact  that  they  arc  somewhat  smaller  than  the  spinal  accessory, 
is  sufficient  to  distinguish  them  from  that  nerve.  They  finally 
disappear  under  the  anterior  border  of  the  trapezius. 


138  HEAD  AND  NECK 

Dissection. — On  the  second  day  after  the  subject  has  been  placed  on  its 
face,  the  trapezius  may  be  reflected.  This  must  be  done  in  conjunction 
with  the  dissector  of  the  arm.  First  separate  the  muscle  from  the  occipital 
bone,  and  then  divide  it  about  half  an  inch  from  the  spines  of  the  vertebrae. 
The  muscle  can  now  be  raised  and  thrown  outwards  towards  its  insertion. 
On  its  deep  surface  the  spinal  accessory  nerve,  the  cervical  nerves  of  supply, 
and  the  superficial  cervical  artery  will  be  noticed.  It  is  the  duty  of  the 
dissector  of  the  upper  limb  to  dissect  these,  but  the  dissector  of  the  head 
and  neck  should  trace  the  superficial  cervical  artery  to  its  origin  from  the 
transversalis  colli. 

The  attachments  of  the  levator  anguli  scapuhe  must  also  be  defined. 
Two  nerve  twigs  from  the  cervical  plexus,  which  lie  on  its  surface  and 
finally  enter  its  substance,  have  already  been  secured.  Further,  passing 
downwards  under  cover  of  this  muscle,  the  ne7've  to  the  rhomboids  and  the 
posterior  scapular  artery  will  be  found.  Almost  invariably  the  nerve  to  the 
rhomboids  gives  one  or  two  twigs  to  the  levator  anguli  scapulae. 

Levator  Anguli  Scapulae  (levator  scapulae). — This  muscle 
arises  by  four  slips  from  the  posterior  tubercles  of  the 
transverse  processes  of  the  upper  four  cervical  vertebrae. 
These  unite  to  form  an  elongated  muscle  which  extends 
downwards  and  backwards  to  be  inserted  into  that  portion 
of  the  vertebral  border  of  the  scapula  which  is  placed  above 
the  root  of  the  spine.  As  already  noted,  the  nerve-supply  of 
the  levator  anguli  scapulae  comes  from  the  third  and  fourth 
cervical  nerves,  and  also  from  the  nerve  to  the  rhomboids. 

Transversalis  Colli  Artery. — This  vessel  will  be  seen 
terminating  near  the  outer  margin  of  the  levator  anguli 
scapulae,  by  dividing  into  the  superficial  cervical  and  posterior 
scapular  arteries.  The  former  of  these  proceeds  upon  the 
superficial  aspect  of  the  levator  anguli  scapulae,  whilst  the 
latter  passes  under  cover  of  that  muscle.  It  is  the  duty  of 
the  dissector  of  the  upper  limb  to  trace  the  further  course  of 
these  branches  of  the  transversalis  colli  artery. 

Dissection. — The  posterior  belly  of  the  omo-hyoid  muscle,  and  the 
suprascapular  artery  and  nerve,  can  now  be  displayed  by  dissecting 
towards  the  upper  margin  of  the  scapula.  This  dissection  must  be  carried 
out  in  conjunction  with  the  dissector  of  the  upper  limb,  and  it  is  well  not 
to  expose  these  structures  at  the  present  stage  for  more  than  an  inch  from 
the  upper  border  of  the  scapula. 

Posterior  Belly  of  the  Omo-hyoid. — This  is  a  slender 
muscular  band  which  arises  from  the  upper  border  of  the 
scapula,  immediately  behind  the  suprascapular  notch.  It 
also  derives  fibres  from  the  ligament  which  bridges  across 
this  notch.  The  further  connexions  of  the  omo-hyoid  will 
be  studied  in  the  dissection  of  the  triangles  of  the  neck  after 
the  body  has  been  turned. 


DORSAL  ASPECT  OF  THE  TRUNK  139 

Suprascapular  Artery  and  Nerve.  —  The  suprascapular 
artery  will  be  noticed  to  enter  the  supraspinous  fossa  of  the 
scapula,  by  passing  over  the  suprascapular  ligament.  The 
suprascapular  ?ien*e,  on  the  other  hand,  is  carried  into  the 
fossa  under  cover  of  the  ligament. 

The  second  day's  work  is  now  completed,  and  on  the  same  day  the 
dissector  of  the  upper  limb  must  finish  his  share  of  the  dissection  of  the 
back,  so  as  to  allow  the  dissector  of  the  head  and  neck  to  begin  the 
examination  of  the  deeper  structures  on  the  dorsal  aspect  of  the  trunk. 

Two  days  are  allowed  for  this  dissection,  and  these  may  be  disposed 
of  in  the  following  manner  : — On  the  first  day,  all  the  muscles,  fascia, 
nerves,  and  blood  vessels  of  the  back,  with  the  exception  of  those  in 
connection  with  the  sub -occipital  triangle,  should  be  studied;  on  the 
second  day,  the  sub-occipital  space  must  be  examined,  and  the  spinal  cord 
displayed.  Should  the  dissector  find  that  the  work  is  greater  than  he  can 
undertake  in  the  allotted  time,  the  sub-occipital  space  may  be  left  over 
until  the  head  and  neck  is  removed  from  the  trunk. 

Serrati  Muscles. — These  are  two  thin  sheets  of  fleshy 
fibres,  which  are  placed  upon  the  posterior  aspect  of  the 
thoracic  wall.  The  serratus  posticus  superior  (serratus  posterior 
superior)  is  much  the  smaller  of  the  two ;  it  arises  by  a  thin 
aponeurotic  tendon — (1)  from  the  lower  part  of  the  ligamentum 
nuchae ;  (2)  from  the  spinous  process  of  the  seventh  cervical 
vertebra ;  and  (3)  from  the  spinous  processes  of  the  upper 
two  or  three  dorsal  vertebrae.  From  this  origin  it  proceeds 
obliquely  downwards  and  outwards,  and  is  inserted  by 
distinct  digitations  into  the  outer  surfaces  of  four  ribs — viz., 
the  second,  third,  fourth,  and  fifth — a  short  distance  in  front 
of  their  angles. 

The  serratus  posticus  inferior  (serratus  posterior  inferior) 
will  be  brought  into  view  by  raising  and  throwing  inwards 
that  portion  of  the  latissimus  dorsi  which  the  dissector  of 
the  upper  limb  has  left  attached  to  the  lumbar  fascia.  The 
serratus  posticus  inferior  will  then  be  observed  to  take 
origin  from  the  spinous  processes  of  the  last  two  dorsal 
and  upper  two  lumbar  vertebrae,  as  well  as  from  the 
supraspinous  ligaments  which  stretch  between  these  bony 
prominences.  The  dissector  will  note,  however,  that  this 
is  not  an  independent  and  distinct  attachment,  but  that  it 
is  effected  through  the  medium  of  the  vertebral  aponeurosis 
and  posterior  lamella  of  the  lumbar  fascia,  with  both  of 
which  the  aponeurotic  tendon  of  the  muscle  blends.  The 
serratus  posticus  inferior  is  directed  upwards  and   outwards, 


i4o  HEAD  AND  NECK 

and  is  inserted  by  four  digitations  into  the  lower  borders  of 
the  four  lower  ribs. 

Vertebral  Aponeurosis. — The  connections  of  the  vertebral 
aponeurosis  can  be  easily  made  out.  It  is  the  strong  but 
thin  and  transparent  fascia  which  bridges  across  the  hollow 
between  the  spinous  processes  of  the  dorsal  vertebrae  and 
the  portions  of  the  ribs  which  lie  internal  to  their  angles. 
It  confines  in  this  hollow  the  proper  muscles  of  the  spine  and 
head.  Make  a  transverse  incision  through  it  about  the 
middle  of  the  dorsal  region,  and  introduce  under  it  the 
handle  of  a  knife.  By  carrying  this  first  in  an  inward  and 
then  in  an  outward  direction,  the  attachment  of  the  apo- 
neurosis to  the  spines  of  the  dorsal  vertebrae  and  to  the 
angles  of  the  ribs  will  be  rendered  manifest.  In  the  next 
place,  note  that  when  it  is  followed  in  an  upward  and  down- 
ward direction  the  fascia  presents  a  different  relation  to  the 
two  serrati  muscles.  Superiorly,  it  proceeds  under  cover  of 
the  serratus  posticus  superior  and  the  splemus  muscles,  and 
is  lost  in  the  deep  layers  of  fascia  of  the  neck ;.  inferiorly,  it 
blends  with  the  aponeurotic  tendons  of  the  serratus  posticus 
inferior  and  the  latissimus  dorsi,  and  with  these  forms  the 
posterior  lamella  of  the  lumbar  fascia. 

Lumbar  Fascia. — The  lumbar  fascia  is  an  exceedingly 
dense  aponeurotic  structure,  which  gives  great  support  to  the 
muscles  of  the  loins,  and  also  serves  as  a  means  of  origin  for 
two  of  the  flat  muscles  of  the  abdominal  wall — viz.,  the 
transversalis  abdominis  and  obliquus  internus.  It  is  attached 
internally  to  the  vertebral  column  by  three  distinct  lamellae, 
which  are  separated  from  each  other  by  intervening  muscular 
masses.  The  posterior  or  superficial  lamella  is  at  present  seen 
in  the  form  of  a  strong  opaque  aponeurotic  sheet  stretching 
outwards  from  the  lumbar  spines.  It  is  formed,  as  we  have 
already  observed,  by  a  continuation  downwards  of  the  verte- 
bral aponeurosis,  and  by  a  union  of  this  with  the  aponeurotic 
tendons  of  the  latissimus  dorsi  and  the  serratus  posticus 
inferior.  Divide  this  lamella  in  a  longitudinal  direction 
about  one  inch  external  to  the  middle  line,  and  raise  it 
from  the  subjacent  erector  spinas  muscle. 

Mesially  it  will  be  seen  to  have  a  strong  attachment  to 
the  tips  of  the  lumbar  spines  and  the  intervening  supra- 
spinous ligaments,  whilst  inferiorly  it  is  fixed  to  the  back  part 
of  the   crest   of  the   ilium,   and  to  the  subjacent  tendon   of 


DORSAL  ASPECT  OF  THE  TRUNK 


141 


the  erector  spinae,  where  this  lies  upon  the  dorsum   of  the 
sacrum. 

The  erector  spinas  should  now  be  pushed  inwards  either 
with  the  fingers  or  with  the  handle  of  a  knife.  This  pro- 
ceeding will  bring  into  view  the  second  or  middle  lamella 
of  the  lumbar  fascia.  Further,  the  union  of  the  posterior 
and  middle  lamellae  beyond  the  outer  border  of  the  erector 
spinae,  and  the  attachment  of  the  middle  lamella  to  the  tips 
of  the  transverse  processes  of  the  lumbar  vertebrae,  may  be 
seen.      Note,    however,   that   whilst   the    main    attachment  of 


Serratus 
post.  inf. 


^- — Erector  spinae 


Quadratus 
lumborum 


Trans versalis   (---Kg 

Internal  \    f| 

oblique  \    * 

External  \ 

oblique  \ 

Fascia 
transversalis""" 


FlG.  64. — Diagram  to  show  the  Connections  of  the  Lumbar  Fascia. 


this  lamella  is  to  the  apices  of  the  transverse  processes,  it 
also  extends  inwards  between  them  and  is  attached  to  their 
contiguous  margins.  The  next  step  consists  in  dividing  the 
middle  lamella  longitudinally  close  to  its  vertebral  attach- 
ment. The  quadratus  lumborum  is  then  brought  into  view, 
and  gently  raising  the  middle  lamella  from  the  surface  of 
this  muscle  until  its  outer  border  is  exposed,  the  whole 
muscle  should  be  pushed  inwards.  This  brings  into  view 
the  third  or  (Ulterior  lamella  of  the  lumbar  fascia,  and  its 
junction  on  the  one  hand  with  the  middle  lamella,  and  on 
the  other  with  the  bodies  of  the  lumbar  vertebrae  close  to 
the  roots  of  the  transverse  processes,  can  be  made  out. 


142  HEAD  AND  NECK 

The  lumbar  fascia,  therefore,  is  formed  at  the  outer 
borders  of  the  erector  spinae  and  quadratus  lumborum 
muscles  by  the  union  of  these  three  lamellae.  Superiorly, 
it  is  attached  to  the  last  rib ;  inferiorly,  it  is  fixed  to  the 
crest  of  the  ilium  ;  whilst  externally  it  is  continued  into  the 
transversalis  abdominis  muscle,  of  which  it  may  be  con- 
sidered to  be  the  posterior  aponeurosis.  By  its  superficial 
surface  it  gives  origin  to  fibres  of  the  internal  oblique  muscle 
of  the  abdominal  wall. 

Dissection. — The  serratus  posticus  superior  must  be  divided  close  to 
its  origin  from  the  vertebral  spines*,  and  turned  outwards  in  order  that 
the  splenius  muscle  may  be  displayed. 

Splenius  Muscle. — The  splenius  has  a  continuous  origin 
from  rather  more  than  the  lower  half  of  the  ligamentum 
nuchas,  and  from  the  spines  of  the  seventh  cervical  and 
upper  six  dorsal  vertebrae.  From  this  the  fibres  pass 
obliquely  upwards  and  outwards  in  the  form  of  a  thick, 
flat  muscle,  which  soon  divides  into  a  cervical  and  a 
cranial  portion.  These  are  termed  respectively  the  splenius 
colli  and  the  splenius  capitis. 

The  splenius  colli  (splenius  cervicis)  turns  forwards  and 
is  inserted,  behind  the  levator  anguli  scapulae,  by  tendinous 
slips,  into  the  posterior  tubercles  of  the  transverse  processes 
of  the  upper  two  or  three  cervical  vertebrae. 

The  splenius  capitis  passes  under  cover  of  the  upper  part 
of  the  sterno-mastoid  muscle,  and  gains  insertion  into  the 
lower  part  of  the  mastoid  process  and  into  the  outer 
portion  of  the  superior  curved  line  of  the  occipital  bone. 
To  obtain  a  view  of  this  insertion,  the  sterno-mastoid 
muscle  may  be  divided  along  the  superior  curved  line 
of  the  occipital  bone  as  far  as  the  mastoid  process.  Upon 
no  account,  however,  detach  it  from  the  mastoid  process. 

Dissection. — The  erector  spinas  and  complexus  muscles  must  now  be 
dissected.  Begin  by  reflecting  the  splenius  muscle.  Detach  it  from  its 
origin  and  throw  it  outwards  and  upwards  towards  its  insertion.  In 
doing  this,  preserve  the  cutaneous  branches  of  the  cervical  nerves  which 
pierce  it. 

When  the  splenius  capitis  is  fully  reflected,  a  small  triangular  space 
will  be  noticed  close  to  the  superior  curved  line  of  the  occipital  bone. 
In  front,  it  is  bounded  by  the  trachelo-mastoid  muscle  ;  behind,  by  the 
outer  border  of  the  complexus  ;  and  above,  by  the  superior  curved  line 
of  the  occipital  bone.  The  floor  of  this  little  space  is  formed  by  the 
superior  oblique  muscle  of  the  head,  and  it  is  traversed  by  the  occipital 
artery,  which  in  this  part  of  its  course  gives  off  its  arteria  princeps 
cervicis  branch. 


DORSAL  ASPECT  OF  THE  TRUNK  143 

Next  remove  the  vertebral  aponeurosis  and  turn  the  latissimus  dorsi, 
the  serratus  posticus  inferior,  and  the  superficial  lamella  of  the  lumbar 
fascia  outwards. 

Erector  Spinae  (sacro -spinalis).  —  Under  this  name  we 
include  a  series  of  muscular  strands  which  stretch  with  a 
greater  or  less  degree  of  continuity  along  the  entire  length 
of  the  dorsal  aspect  of  the  spinal  column.  In  the  lumbar 
region  it  constitutes  a  bulky  fleshy  mass  which  may  be 
considered  the  starting-point.  This  bulky  mass  sends  a 
pointed  process  downwards  on  the  back  of  the  sacrum,  and 
has  the  following  origin: — (1)  from  the  spines  of  the  lower 
two  dorsal,  all  the  lumbar,  and  all  the  sacral  vertebrae;  (2) 
from  the  supraspinous  ligaments  which  bind  the  lumbar  and 
dorsal  spines  together;  (3)  from  the  back  of  the  sacrum  and 
from  the  posterior  sacro-iliac  ligament ;  (4)  from  the  posterior 
fifth  of  the  iliac  crest.  In  great  part  the  superficial  surface 
of  this  muscular  mass  is  covered  by  a  very  dense  tendon, 
which  in  its  lower  part  becomes  blended,  as  already  noted, 
with  the  superficial  lamella  of  the  lumbar  fascia. 

As  the  erector  spinae  is  followed  upwards  it  is  seen  to 
divide  into  three  columns.  The  outer  column  first  separates 
from  the  general  mass,  and  to  it  the  name  of  ilio-costalis  is 
given  ;  the  middle  column  is  termed  the  longissiinns  dorsi ; 
and  the  inner  column,  which  only  becomes  quite  distinct 
as  we  approach  the  upper  part  of  the  dorsal  region,  is  called 
the  spifialis  dorsi. 

Ilio-costalis  (ilio-costalis  lumborum). — The  intermuscular 
interval  between  this  muscle  and  the  longissimus  becomes 
apparent  about  the  level  of  the  last  rib.  The  separation  is 
rendered  all  the  more  distinct  by  the  external  branches  of  the 
posterior  primary  divisions  of  the  dorsal  spinal  nerves  which 
appear  in  the  interval. 

Turn  the  muscle  outwards  with  the  handle  of  the  knife,  and  clean  its  slips 
of  insertion.     The  nerves  must  at  the  same  time  be  carefully  preserved. 

The  ilio-costalis  will  now  be  observed  to  end  in  six  or 
seven  tendinous  slips,  which  are  inserted  into  the  angles  of 
the  six  or  seven  lower  ribs.  But  wherever  the  ilio-costalis 
drops  one  of  these  slips,  another  tendinous  slip  takes  origin 
from  the  upper  border  of  the  same  rib.  In  this  way  a  second 
muscle  is  formed,  which  continues  the1  outer  column  of  the 
erector  spinae  upwards.  This  muscle  is  called  the  musculus 
accessorius. 


i44  HEAD   AND   NECK 

Musculus  Accessorius  (ilio-costalis  dorsi). — The  musculus 

accessorius,  therefore,  arises  close  to  the  inner  side  of  the 
ilio-costalis  by  six  tendinous  slips  from  the  upper  borders  of 
the  six  lower  ribs.  It  terminates  in  tendons  which  are  in- 
serted into  the  angles  of  the  upper  six  ribs,  and  also  into  the 
transverse  process  of  the  lowest  cervical  vertebra. 

Cervicalis  Ascendens  (ilio-costalis  cervicis). — This  muscle 
may  be  looked  upon  as  the  continuation  of  the  outer  column 
upwards  into  the  neck.  It  arises  close  to  the  inner  side  of 
the  accessorius  by  four  slips  from  the  third,  fourth,  fifth,  and 
sixth  ribs,  and  is  inserted  into  the  posterior  tubercles  of  the 
transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical 
vertebrae. 

Longissimus  Dorsi. — The  longissimus  dorsi  is  the  largest 
of  the  three  divisions  into  which  the  erector  spinae  splits,  and 
it  extends  upwards  as  high  as  the  first  dorsal  vertebra.  It  is 
inserted  by  two  distinct  rows  of  tendinous  and  fleshy  slips. 
The  inner  row  consists  of  a  series  of  tendons  attached  in  the 
dorsal  region  to  the  tips  of  the  transverse  processes  of  all 
the  dorsal  vertebrae,  and  in  the  loin  to  the  accessory  processes 
of  the  lumbar  vertebrae  ;  the  outer  row  is  composed  of  fleshy 
slips,  which  are  inserted  in  the  dorsal  region  into  the  lower 
ten  ribs,  midway  between  their  tubercles  and  angles,  and  in 
the  loin  to  the  transverse  processes  of  the  lumbar  vertebrae 
and  to  the  middle  layer  of  the  lumbar  fascia.  But  this 
muscular  column  does  not  end  in  the  dorsal  region  ;  it  is 
carried  up  into  the  neck,  and  even  reaches  as  high  as  the 
mastoid  process  of  the  skull  by  two  muscular  continuations 
termed  respectively — (i)  the  transversalis  cervicis,  and  (2) 
the  trachelo-mastoid. 

Transversalis  Cervicis  (longissimus  cervicis). — The  trans- 
versalis cervicis  muscle  takes  origin  in  the  upper  dorsal 
region,  by  four  or  five  slips  from  the  transverse  processes  of 
a  corresponding  number  of  the  upper  dorsal  vertebrae,  and  it 
gains  insertion  into  the  posterior  tubercles  of  the  transverse 
processes  of  all  the  cervical  vertebrae,  with  the  exception  of 
the  first  and  the  last. 

Trachelo-mastoid  (longissimus  capitis). — The  trachelo- 
mastoid  is  prolonged  upwards  in  the  neck  under  cover  of  the 
splenius.  Its  origin  from  the  transverse  processes  of  three 
or  four  of  the  upper  dorsal  vertebrae  is  intimately  associated 
with   that   of  the  transversalis  cervicis.      In    addition   to    its 


DORSAL  ASPECT  OF  THE  TRUNK  145 

dorsal  origin,  however,  it  also  draws  three  or  four  slips  from 
the  articular  processes  of  a  like  number  of  the  lower  cervical 
vertebras.  The  narrow  fleshy  band  which  results  is  inserted 
into  the  back  part  of  the  mastoid  process,  under  cover  of  the 
splenius  capitis  and  sterno-mastoid  muscles. 

Spinalis  Dorsi.  —  This,  the  innermost,  shortest,  and 
weakest  of  the  three  columns,  is  in  some  respects  the  most 
difficult  to  define.  Below,  it  is  intimately  blended  with  the 
longissimus  dorsi,  but  it  may  be  regarded  as  taking  origin  by 
four  tendons  from  the  spines  of  the  two  upper  lumbar  and 
two  lower  dorsal  vertebrae.  These,  by  theip  union,  form  a 
small  muscle,  which  is  inserted  by  a  series  of  slips  into  a  very 
variable  number  of  the  upper  dorsal  spines.  It  is  closely 
connected  with  the  subjacent  semispinalis  dorsi. 

Dissection. — The  occipital  artery  has  already  been  observed  crossing 
the  apex  of  the  posterior  triangle  (p.  137),  and  its  terminal  branches  have 
been  dissected  as  they  ramify  in  the  scalp  (p.  112).  The  second  part  of 
the  vessel,  which  extends  from  under  shelter  of  the  mastoid  process,  along 
the  superior  curved  line  of  the  occipital  bone,  to  the  point  where  it  pierces 
the  trapezius  to  become  superficial,  can  now  be  fully  exposed.  To  effect 
this,  the  trachelo-mastoid  must  be  divided  a  short  distance  below  its 
insertion,  and  along  with  the  splenius  capitis  thrown  upwards  as  far  as 
possible. 

Occipital  Artery  (arteria  occipitalis). — The  second  part 
of  the  occipital  artery  is  now  displayed.  In  the  region  of 
the  mastoid  process  it  is  very  deeply  placed ;  indeed,  no  less 
than  five  structures  lie  superficial  to  it.  These  are  (enumer- 
ating them  in  order  from  the  vessel  outwards) — (1)  the  origin 
of  the  posterior  belly  of  the  digastric  muscle  ;  (2)  the  mastoid 
process ;  (3)  the  trachelo-mastoid ;  (4)  the  splenius  capitis  ; 
and  (5)  the  sterno-mastoid.1  As  the  artery  runs  backwards, 
it  very  soon  emerges  from  under  cover  of  the  first  three  of 
these  structures,  and  a  little  farther  on  it  leaves  the  shelter  of 
the  splenius ;  so  that  it  is  covered  by  the  sterno-mastoid 
alone.  Issuing  from  under  cover  of  the  posterior  border  of 
this  muscle,  the  artery  crosses  the  apex  of  the  posterior 
triangle,  and  disappears  under  the  trapezius,  which  it  finally 
pierces  near  the  external  occipital  protuberance,  to  reach  the 
scalp.  Two  muscles  constitute  its  deep  relations — viz.,  the 
insertion  of  the  superior  oblique  and  the  complexus. 


1   It  is  not  uncommon  to  find  the  artery  at  this  point  of  its  course  nearer 
It  may  pass  backwards  between  the  splenius  and  the  trachelo- 
mastoid. 

VOL.   II — 10 


1 46  HEAD  AND   NECK 

The  following  branches  may  be  traced  from  this  portion  of 
the  occipital  artery  : — 

i.   Arteria  princeps  cervicis. 

2.  Mastoid. 

3.  Muscular. 

The  arteria  prijiceps  cervicis  (ramus  descendens)  is  a  twig 
of  some  size,  which  passes  inwards  to  the  outer  border  of  the 
complexus.  Here  it  divides  into  a  superficial  and  a  deep 
branch.  The  former  ramifies  on  the  surface  of  the  com- 
plexus, whilst  the  latter  pursues  a  deeper  course.  It  sinks 
under  cover  of  that  muscle,  and  will  be  followed  to  its  destina- 
tion at  a  later  stage  in  the  dissection. 

The  small  mastoid  artery  (ramus  mastoideus)  enters  the 
posterior  cranial  fossa  through  the  mastoid  foramen,  and 
supplies  the  dura  mater  and  cranial  wail  in  this  region. 

The  muscular  twigs  go  to  the  neighbouring  muscles. 

The  veins  corresponding  to  the  occipital  artery  are  two, 
or  perhaps  three,  in  number.  They  drain  the  blood  from  the 
occipital  portion  of  the  scalp,  and  open  into  the  vertebral  and 
deep  cervical  veins.  The  outermost  of  the  occipital  veins 
effects,  as  a  general  rule,  a  communication  (emissarium 
mastoideum)  with  the  lateral  sinus  through  the  mastoid 
foramen. 

Dissection. — In  cleaning  the  complexus  muscle,  and  in  defining  its 
attachments,  care  must  be  taken  of  the  internal  branches  of  the  posterior 
primary  divisions  of  the  second,  third,  fourth,  and  fifth  cervical  nerves. 
The  first  of  these — or,  in  other  words,  the  great  occipital — from  its  great 
size,  runs  little  risk  of  injury,  but  the  others  are  liable  to  be  overlooked. 
They  all  emerge  from  the  substance  of  the  muscle  close  to  the  mesial  plane. 

Complexus. — The  complexus  muscle,  placed  in  the  cervical 
and  upper  dorsal  regions,  inclines  obliquely  upwards  and 
inwards  to  its  insertion  into  the  occiput.  It  arises  by  tendin- 
ous slips  from  the  transverse  processes  of  the  upper  six  dorsal 
vertebrae,  and  by  three  slips  from  the  articular  processes  of 
the  fourth,  fifth,  and  sixth  cervical  vertebrae.  A  thick  fleshy 
muscle  is  thus  formed,  and  this  is  inserted  into  a  large,  some- 
what oval  impression  between  the  superior  and  inferior  curved 
lines  of  the  occipital  bone,  close  to  its  crest.  The  muscle 
narrows  somewhat  as  it  passes  upwards,  and  is  separated  from 
its  neighbour  of  the  opposite  side  by  the  ligamentum  nuchae. 

The  inner  portion  of  the  muscle,  which  is  to  a  certain 
extent  distinct  from  the  general  mass,  and  is  divided  into  two 


DORSAL  ASPECT  OF  THE  TRUNK 


i47 


bellies  by  an  intermediate  tendon,  is  frequently  designated  the 
biventer  cervicis. 

Dissection. — The  com  plexus  must  now  be  reflected  by  detaching  it  from 
the  occiput  and  throwing  it  outwards.  This  dissection  requires  care,  not 
only  on  account  of  the  nerves  which  have  been  seen  to  perforate  it  to  reach 
the  surface,  but  also  on  account  of  the  structures  which  it  covers.  In  its 
upper  part  it  lies  over  the  sub-occipital  triangle  and  the  muscles  bounding 
it,  whilst  below  it  covers  the  semispinalis  muscle.  A  thick  dense  fascia  is 
placed  over  these  subjacent  parts,  and  in  this  we  find  certain  of  the  cervical 


Posterior  occipito- 
atlantoid  ligament 

Sub-occipital  nerve 
Great  occipital  nerve — J 


Vertebral  artery 

Anterior  primary 

division  of  spinal 

nerve 


terior  arch  of  atlas 
igamentum  nucha; 


Posterior  primary  divisions 
of  spinal  nerves 


Fig.  65. 


L— Seventh  cervical  vertebra 


-Dissection  of  the  Ligamentum  Nucha:  and  of  the 
Vertebral  Artery  in  the  Neck. 


nerves  and  the  anastomosis  between  the  arteria  princeps  cervicis  and  arteria 
profunda  cervicis.  The  dissector  must  specially  look  for  a  small  twig  from 
the  sub-occipital  nerve  which  enters  the  deep  surface  of  the  upper  part  of 
the  complexus,  and  for  a  larger  branch  to  the  same  muscle  from  the  great 
occipital  nerve.  The  inner  margin  of  the  complexus  will  be  seen  to  be  in 
contact  with  a  mesial  fibrous  partition  which  separates  it  from  the  corre- 
sponding muscle  of  the  opposite  side.     This  is  the  ligamentum  nuchae. 

Ligamentum  Nuchae  (Fig.  65). — This  is  a  strong  fibrous 
partition  placed  in  the  mesial  plane  between  the  muscles  on 
each  side  of  the  back  of  the  neck.  It  represents  a  powerful 
clastic  structure  in  quadrupeds,  which  helps  to  sustain  the  weight 
of  the  dependent  head.  In  man,  however,  there  is  not  much 
11 — 10  a 


148  HEAD  AND   NECK 

elastic  tissue  developed  in  connexion  with  it,  and  it  appears 
to  be  a  continuation  upwards  of  the  supraspinous  ligament 
from  the  spine  of  the  seventh  cervical  vertebra  to  the  external 
occipital  protuberance.  In  shape  it  is  somewhat  triangular. 
By  its  base  it  is  attached  to  the  crest  of  the  occipital  bone ; 
by  its  anterior  border  it  is  fixed  by  a  series  of  slips  to  the 
posterior  tubercle  of  the  atlas,  and  to  the  bifid  spines  of  the 
cervical  vertebrae  in  the  intervals  between  their  tubercles.  Its 
apex  is  formed  by  its  attachment  to  the  spine  of  the  seventh 
cervical  vertebra,  whilst  its  posterior  border  is,  in  a  measure, 
free,  and  gives  origin  to  the  trapezius,  rhomboid,  serratus 
posticus  superior,  and  splenius  muscles. 

Arteria  Princeps  Cervicis  and  Arteria  Profunda  Cervicis. 
— The  deep  cervical  artery  springs  from  the  superior  intercostal 
branch  of  the  subclavian,  and  reaches  the  dorsum  by  passing 
backwards  between  the  transverse  process  of  the  last  cervical 
vertebra  and  the  neck  of  the  first  rib.  At  the  present  stage 
of  the  dissection  it  is  seen  ascending  upon  the  semispinalis 
colli  muscle  and  anastomosing  with  the  arteria  princeps  cervicis. 
The  latter  artery,  as  we  have  seen,  is  a  branch  of  the  occipital. 
Both  vessels  likewise  anastomose  with  twigs  from  the  vertebral 
artery. 

The  arteria  profunda  cervicis  is  accompanied  by  a  large 
vein — the  vena  profunda  cervicis.  This  vessel  begins  in  the 
sub-occipital  region,  where  it  is  joined  by  the  occipital  veins, 
and  it  ends  in  the  vertebral  vein  close  to  its  termination.  It 
reaches  this  point  by  turning  forwards  under  the  transverse 
process  of  the  last  cervical  vertebra. 

Posterior  Primary  Divisions  of  the  Spinal  Nerves. — The 
nerves  of  the  back  must  now  be  examined.  They  are  the 
posterior  primary  divisions  of  the  spinal  nerves.  With  four 
exceptions  (viz.,  the  first  cervical,  fourth  and  fifth  sacral,  and 
the  coccygeal  nerves),  each  posterior  division  will  be  found  to 
divide  into  an  external  and  an  internal  branch. 

Examine  these  nerves  successively  in  the  cervical,  dorsal,  and  lumbar 
regions.  It  is  well,  however,  to  defer  the  dissection  of  the  sacral  and 
coccygeal  nerves  until  the  multifidus  spinae  muscle  has  been  studied. 

Cervical  Region. — Here  the  posterior  primary  divisions 
of  the  spinal  nerves  are  eight  in  number.  The  posterior 
division  of  the  first  or  sub-occipital  nerve,  which,  as  we  have 
seen,  fails  to  divide  into  an  external  and  an  internal  branch, 


DORSAL  ASPECT  OF  THE  TRUNK  149 

lies  deeply  in  the  sub-occipital  triangle,  and  will  be  examined 
when  this  space  is  dissected. 

The  posterior  primary  division  of  the  second  cervical  nerve 
is  very  large,  and  appears  between  the  neural  arches  of  the 
atlas  and  axis  vertebrae.  The  posterior  primary  divisions  of 
the  succeeding  six  cervical  nerves  arise  from  the  corresponding 
spinal  nerve-trunks  in  the  intervertebral  foramina  a  short 
distance  farther  out,  and,  turning  backwards  under  cover  of 
the  posterior  intertransverse  muscles,  appear  in  the  intervals 
between  the  transverse  processes. 

The  external  branches  are  of  small  size,  and  are  entirely 
devoted  to  the  supply  of  muscles.  They  give  twigs  to  the 
splenius  colli  and  to  the  cervical  and  cranial  prolongations  of 
the  erector  spinae. 

The  internal  branches  are  not  all  distributed  alike,  nor 
indeed  do  they  present  the  same  relations.  Those  from  the 
second,  third,  fourth,  and  fifth  nerves  run  inwards  towards  the 
spinous  processes,  superficial  to  the  semispinalis  colli  muscle, 
and  under  cover  of  the  complexus.  When  close  to  the  mesial 
plane  they  turn  backwards,  pierce  the  complexus,  splenius, 
and  trapezius  muscles,  and  become  superficial.  In  their 
course  to  the  surface  they  give  numerous  twigs  to  the  neigh- 
bouring muscles. 

The  internal  branch  of  the  second  nerve  is  remarkable  for 
its  large  size.  It  receives  the  special  name  of  great  occipital. 
It  will  be  noticed  turning  round  the  lower  border  of  the 
inferior  oblique  muscle,  to  which  it  supplies  some  twigs.  In 
passing  to  the  surface  it  pierces  the  complexus  and  trapezius. 
To  the  former  it  gives  several  twigs.  The  distribution  of  this 
nerve  on  the  occiput  has  already  been  noticed  (p.  no). 

The  internal  branch  of  the  third  nerve  likewise  sends  an 
offset  to  the  occipital  portion  of  the  scalp  (p.  135). 

The  internal  branches  of  the  lower  three  posterior  divisions 
of  the  cervical  nerves  resemble  the  preceding,  in  so  far  that 
they  take  a  course  inwards  towards  the  spinous  processes. 
They  differ  from  them,  however,  in  running  under  cover  of 
the  semispinalis  muscle,  and  in  being,  as  a  rule,  entirely 
expended  in  the  supply  of  muscles. 

Dorsal  Region. — The  posterior  primary  divisions  of  the 
dorsal  nerves  make  their  appearance  in  the  intervals  between 
the  transverse  processes.  The  external  branches  proceed  out- 
wards under  cover  of  the  middle  column  of  the  erector  spinas 


150  HEAD  AND  NECK 

muscle,  and  appear  in  the  interval  between  the  longissimus 
dorsi  on  the  one  hand,  and  the  ilio-costalis  and  accessorius 
on  the  other.  The  upper  six  or  seven  of  these  nerves  are  ex- 
hausted in  the  supply  of  the  middle  and  outer  columns  of  the 
erector  spinae,  and  the  levatores  costarum ;  the  loiver  five  or 
six,  however,  are  considerably  larger,  and  contain  both  motor 
and  sensory  fibres.  After  giving  up  their  motor  fibres  to  the 
same  muscles,  they  become  superficial,  by  piercing  the  serratus 
posticus  inferior,  and  the  latissimus  dorsi,  in  a  line  with  the 
angles  of  the  ribs.  The  cutaneous  distribution  of  these  nerves 
has  already  been  examined  by  the  dissector  of  the  upper  limb. 

The  internal  branches  are  also  distributed  differently  in  the 
upper  and  lower  portions  of  the  dorsal  region.  The  lower 
five  or  six  are  very  small,  and  end  in  the  multifidus  spinae 
muscle.  The  upper  six  or  seven  pass  inwards  between  the 
multifidus  and  semispinalis,  and  after  supplying  the  muscles 
between  which  they  are  situated,  they  are  directed  backwards, 
and  become  superficial.  In  passing  towards  the  surface  they 
pierce  the  splenius,  rhomboideus,  and  trapezius  muscles,  and 
thus  gain  the  superficial  fascia,  where  they  have  been  already 
dissected. 

Lumbar  Region. — The  internal  bra?iches  of  the  posterior 
divisions  of  the  five  lumbar  nerves  are  of  small  size,  and,  like 
the  corresponding  twigs  in  the  lower  dorsal  region,  they  have 
a  purely  muscular  distribution.  They  end  in  the  multifidus 
spinae  muscle. 

The  external  branches  sink  into  the  substance  of  the  erector 
spinae,  and  are  concerned  in  the  supply  of  that  muscle,  and 
also  of  the  lumbar  intertransverse  muscles.  The  upper  three 
of  these  nerves  are  of  large  size,  and  become  cutaneous  by 
piercing  the  superficial  lamella  of  the  lumbar  fascia.  They 
have  already  been  traced  by  the  dissector  of  the  lower  limb 
to  the  skin  of  the  gluteal  region.  The  lowest  external  branch 
communicates  with  the  corresponding  branch  of  the  first 
sacral  nerve. 

Blood  Vessels  of  the  Back. — In  the  cervical  region  the 
dissector  has  already  noticed  the  arteria  profunda  cervicis, 
the  second  part  of  the  occipital  artery,  and  its  branch  termed 
the  arteria  princeps  cervicis.  Deep  in  the  sub-occipital  region 
he  will  subsequently  meet  with  a  small  portion  of  the 
vertebral  artery.  In  addition  to  these,  however,  minute 
twigs  may  be  discovered,  in  a  well-injected  subject,  passing 


DORSAL  ASPECT  OF  THE  TRUNK  151 

backwards  from  the  vertebral  artery  in  the  intervals  between 
the  transverse  processes,  and  also  in  the  sub-occipital  space. 
These  supply  the  muscles,  and  anastomose  with  the  other 
arteries  in  this  region. 

In  the  dorsal  regio?i  the  dorsal  branches  of  the  aortic  inter- 
costal arteries  make  their  appearance  between  the  transverse 
processes.  Each  of  these  vessels  reaches  this  point  by 
passing  backwards  in  the  interval  between  the  body  of  a 
vertebra  and  the  superior  costo-transverse  ligament.  It  is 
associated  with  the  corresponding  posterior  primary  division 
of  a  spinal  nerve,  and  with  it  is  distributed  to  the  muscles 
and  integument  of  the  back. 

In  the  lumbar  region  similar  branches  are  derived  from  the 
lumbar  arteries.      They  are  distributed  in  the  same  manner. 

In  both  dorsal  and  lumbar  regions  these  vessels,  before 
reaching  the  back,  furnish  small  spinal  branches  which  enter 
the  spinal  canal  through  the  intervertebral  foramina.  These 
will  be  traced  at  a  later  period. 

The  accompanying  veins  of  the  dorsal  branches  of  the 
lumbar  and  intercostal  arteries  pour  their  blood  into  the 
lumbar  and  intercostal  veins.  These  veins  are  of  large  size, 
being  joined  by  tributaries  from  the  dorsal  spinal  venous 
plexus,  and  also  by  others  from  the  interior  of  the  spinal  canal. 

Transversus  Spinalis. — Under  this  name  are  included  a 
system  of  muscles  which  occupy  the  vertebral  groove  from 
the  back  of  the  sacrum  as  high  as  the  axis  vertebra.  When 
this  muscular  mass  is  analysed,  it  is  found  to  consist  of  three 
strata,  each  of  which  is  composed  of  a  series  of  bundles  or 
slips  pursuing  a  more  or  less  oblique  course.  As  the  term 
given  to  the  whole  system  implies,  these  slips  for  the  most 
part  stretch  from  the  transverse  processes  upwards  and  in- 
wards to  be  inserted  into  the  spinous  processes  of  the  vertebrae. 
The  superficial  slips  pass  over  five  or  more  vertebrae  and 
connect  distant  points  on  the  column  ;  the  deeper  slips  are 
shorter,  and  the  most  deeply  placed  of  all  merely  pass  be- 
tween contiguous  vertebrae. 

The  superficial  layer  is  termed  the  semispinalis  muscle;  the 
intermediate  layer  is  called  the  multifidus  spituc ;  whilst  the 
deep  stratum  is  composed  of  a  series  of  short  muscles,  termed 
the  rotatores  spincc.  In  the  dorsal  and  cervical  regions  we 
find  the  three  layers ;  in  the  lumbar  and  sacral  regions  the 
semispinalis  is  absent. 
n—10  6 


152  HEAD  AND  NECK 

Dissection. — The  semispinalis  muscle  is  already  in  great  part  exposed. 
To  display  it  fully,  however,  it  is  necessary  to  remove  the  spinalis  dorsi 
muscle. 

Semispinalis  Muscle. — This  muscle  may  be  described  in 
two  parts — the  semispinalis  dorsi  and  semispinalis  colli. 

The  semispinalis  dorsi  is  composed  of  a  series  of  muscular 
slips,  with  long  tendons  at  either  end,  which  arise  from  the 
transverse  processes  of  five  of  the  lower  dorsal  vertebrae  (viz., 
from  the  sixth  to  the  tenth).  It  is  inserted  into  the  spines  of 
the  upper  four  dorsal  and  lower  two  cervical  vertebras. 

The  semispinalis  colli  lies  under  cover  of  the  complexus. 
It  springs  from  the  transverse  processes  of  the  upper  five 
dorsal  vertebrae,  and  is  inserted  into  the  spines  of  four  cervical 
vertebrae  (viz.,  from  the  second  to  the  fifth). 

The  slips  composing  the  semispinalis  muscle  stretch  over 
five  or  more  vertebrae. 

Dissection. — The  multifidus  spina?  is  of  great  extent.  Beginning  in  the 
sacral  region,  it  passes  upwards  as  far  as  the  axis  vertebra.  It  is  weakly 
developed  in  the  dorsal  region,  but  is  strongly  marked  in  the  loin  and  in 
the  neck — more  especially  in  the  former.  To  bring  it  thoroughly  into 
view,  the  semispinalis  muscle  must  be  detached  from  the  spines  and  thrown 
outwards  :  the  erector  spinas  muscle  must  also  be  separated  from  the 
lumbar  and  sacral  spines  and  drawn  aside — if,  indeed,  this  has  not  been 
already  done  in  following  out  the  nerves. 

Multifidus  Spinse  (multifidus). — In  the  lumbar  and  sacral 
regions  the  multifidus  will  be  seen  to  constitute  a  thick  fleshy 
mass,  which  clings  closely  to  the  vertebral  spines.  In  this 
situation  it  has  a  very  extensive  .origin — viz.,  (i)  from  the 
deep  surface  of  the  aponeurotic  origin  of  the  erector  spinse ; 
(2)  from  the  posterior  surface  of  the  sacrum  as  low  as  the 
fourth  aperture ;  (3)  from  the  posterior  sacro-iliac  ligament ; 
(4)  from  the  posterior  superior  spine  of  the  ilium  ;  and  (5) 
from  the  mammillary  processes  of  the  lumbar  vertebrae.  In 
the  dorsal  region  it  takes  origin  from  the  transverse  processes 
of  the  vertebrae,  and  in  the  cervical  region  from  the  articular 
processes  of  at  least  four  of  the  lower  cervical  vertebrae. 
The  bundles  which  compose  the  multifidus  pass  over  two, 
three,  or  four  vertebrae,  and  are  inserted  into  the  whole  length 
of  the  various  spinous  processes  of  the  movable  vertebrae  as 
high  up  as  the  axis. 

Rotatores  Spinae  (submultifidus). — These  are  a  series  of 
small  muscles  which  may  be  exposed  by  raising  the  multifidus. 
In  the  dorsal  region  each  muscle  springs  from  the  root  of  a 


DORSAL  ASPECT  OF  THE  TRUNK 


00 


transverse  process,  and  is  inserted  into  the  lamina  of  the 
vertebra  immediately  above,  close  to  the  root  of  the  spinous 
process.  Somewhat  similar  muscles  have  been  described  in 
the  cervical  and  lumbar  regions,  and  also  a  series  of  longer 
and  more  superficial  slips  which  connect  alternate  vertebrae 
with  each  other  (Hughes). 

Interspinals  and  Intertransversales. — The  dissector 
should  next  examine  the  minute  interspinous  and  intertrans- 
verse muscles. 

The  interspinous  muscles  can  hardly  be  said  to  exist  in  the 
dorsal  region,  except  in  its  upper  and  lower  parts,  where  they 
are  present  in  a  rudimentary  condition.  In  the  neck  they 
are  arranged  in  pairs  —  two  occupying  each  interspinous 
interval,  with  the  exception  of  that  between  the  axis  and  atlas. 
In  the  lumbar  region  they  are  also  well  marked  and  in  pairs ; 
here  they  are  attached  to  the  whole  length  of  the  spinous 
processes. 

The  ifitertransverse  muscles  (intertransversarii)  are  strongly 
developed  in  the  lumbar  region,  and  occupy  the  entire  length 
of  the  intertransverse  intervals.  Additional  rounded  fasciculi 
may  be  observed  passing  between  the  accessory  processes. 
These  are  termed  the  interaccessorii. 

In  the  dorsal  region  intertransverse  muscles — very  weak 
and  poorly  developed — are  only  found  in  the  lower  three  or 
four  spaces. 

In  the  cervical  region  the  intertransversales  are  present 
in  pairs.  They  will  be  better  examined  at  a  subsequent 
period. 

Levatores  Costarum. — These  constitute  a  series  of  twelve 
fan-shaped  muscles,  which  pass  from  the  transverse  processes 
to  the  ribs.  To  bring  them  thoroughly  into  view,  the  longis- 
simus  dorsi,  ilio-costalis,  and  accessorius  muscles  should  be 
removed.  The  first  muscle  of  the  series  springs  from  the  tip 
of  the  transverse  process  of  the  last  cervical  vertebra,  and, 
expanding  as  it  proceeds  downwards  and  outwards,  is  inserted 
into  the  outer  border  of  the  first  rib,  immediately  beyond  the 
tubercle.  Each  of  the  succeeding  muscles  takes  origin  from 
the  tip  of  a  dorsal  transverse  process,  and  is  inserted  into 
the  outer  surface  of  the  rib  immediately  below,  along  a  line 
extending  from  the  tubercle  to  the  angle. 

Posterior  Primary  Divisions  of  the  Sacral  Nerves. — These 
are  very  small.      The  upper  four  will   be  found  emerging  from 


154  HEAD  AND  NECK 

the  posterior  sacral  foramina ;  the  fifth  appears  at  the  lower 
end  of  the  sacral  canal. 

To  expose  the  upper  three  the  multifidus  spinae  muscle 
covering  the  upper  three  sacral  apertures  must  be  carefully 
removed.  Each  of  these  three  nerves  will  be  found  to 
divide  in  the  usual  manner  into  an  internal  and  external 
branch. 

The  internal  branches  are  very  fine,  and  end  in  the  multi- 
ndus spinae. 

The  external  branches  are  somewhat  larger,  and  join 
together  so  as  to  form  a  looped  plexus  upon  the  back  of  the 
sacrum.  This  communicates  above  with  the  external  branch 
of  the  last  lumbar  nerve  and  below  with  the  posterior  division 
of  the  fourth  sacral  nerve.  Branches  proceed  from  the  loops 
thus  formed  to  the  surface  of  the  great  sacro-sciatic  ligament. 
Finally  they  become  superficial  by  piercing  the  gluteus  maxi- 
mus  muscle,  and  they  supply  a  limited  area  of  skin  over  the 
gluteal  region.  They  have  already  been  examined  by  the 
dissector  of  the  lower  limb. 

The  lowest  two  posterior  primary  divisions  of  the  sacral 
nerves  do  not  exhibit  the  usual  division  into  external  and 
internal  branches.  They  are  very  small,  and,  after  communi- 
cating with  each  other,  and  also  with  the  coccygeal  nerve,  they 
distribute  filaments  to  the  parts  on  the  back  of  the  lower 
portion  of  the  sacrum  and  on  the  dorsal  aspect  of  the  coccyx. 

Minute  twigs  from  the  lateral  sacral  artery  accompany  the 
sacral  nerves  and  anastomose  with  twigs  from  the  gluteal  and 
sciatic  arteries. 

Posterior  Division  of  the  Coccygeal  Nerve. — This  is  a 
slender  twig  which  emerges  from  the  inferior  opening  of  the 
sacral  canal,  and,  after  being  joined  by  a  filament  from  the 
last  sacral  nerve,  is  distributed  on  the  back  of  the  coccyx. 

Dorsal  Spinal  Venous  Plexus. — A  plexus  of  veins  is  situ- 
ated upon  the  superficial  aspect  of  the  neural  arches  of  the 
vertebrae,  subjacent  to  the  multindus  muscle.  This  plexus 
collects  blood  from  the  integument  and  muscles  of  the  back, 
and  in  the  dorsal  and  lumbar  regions  pours  it  into  the  posterior 
tributaries  of  the  intercostal  and  lumbar  veins.  In  the  neck 
it  is  especially  well  marked,  and  its  blood  is  emptied  into  the 
vertebral  veins.  It  is  hardly  to  be  expected,  however,  that 
the  dissector,  in  an  ordinary  dissection,  will  make  out  much 
of  these  venous  channels. 


DORSAL  ASPECT  OF  THE  TRUNK 


*55 


Directions. — The  last  day  upon  which  the  body  is  allowed  to  remain  in 
its  present  position  must  be  devoted  to  the  dissection  of  the  sub-occipital 
triangle,  and  to  the  display  of  the  spinal  cord,  its  membranes,  nerve-roots, 
and  blood-vessels. 

In  the  event  of  the  dissector  being  pushed  for  time,  it  is  better  that  he 
should  proceed  at  once  to  expose  the  spinal  cord,  and  defer  the  dissection 
of  the  sub-occipital  region  until  the  head  and  neck  has  been  removed  from 
the  body. 


Arteria  princeps  cervicis 


Occipital  artery 


Transverse  process 
of  atlas 


Arteria  profunda 
cervicis 


Great  occipital  nerve 


Lywa>^    Superior  oblique 
fflllJl  III  fel*r-r^  muscle 


Rectus  capitis 
posticus  minor 
Sub-occipital  nerve 

Vertebral  artery 

Posterior  arch  of 

atlas 

Rectus  capitis 

posticus  major 

Inferior  oblique 

muscle 

Spine  of  axis 


Semispinalis  colli 


Fig.  66. — Dissection  of  the  Sub-occipital  Region.     Note  that  in  this  specimen 
the  occipital  artery  is  superficial  to  the  trachelo-mastoid  muscle. 


Sub-Occipital  Space. — The  sub-occipital  space  is  a  small 
triangular  area,  exposed  by  the  reflection  of  the  complexus 
muscle.  It  is  boutided  by  three  muscles — viz.,  (i)  the  rectus 
capitis  posticus  major,  which  forms  its  upper  and  inner 
boundary;  (2)  the  obliquus  inferior,  which  limits  it  below; 
and  (3)  the  obliquus  superior,  which  bounds  it  above  and  to 
the  outer  side.  When  dissected,  its  floor  will  be  found  to 
consist  of  two  structures — viz.,  the  posterior  arch  of  the  atlas 


i56  HEAD  AND  NECK 

and  the  thin  posterior  occipito-atlantal  ligament.      It  contains 

within  its  area   a   portion   of   the   vertebral   artery   and    the 

posterior  primary  division  of  the  sub-occipital  or  first  cervical 

nerve. 

Dissection. — Before  cleaning  the  muscles  bounding  the  triangle,  the 
sub-occipital  nerve  must  be  secured.  This  can  best  be  done  by  tracing 
into  the  space  the  minute  twig  which  it  has  been  seen  to  give  to  the  deep 
surface  of  the  complexus,  or,  if  this  has  not  been  observed,  by  endeavouring 
to  find  the  twig  which  it  gives  to  the  rectus  capitis  posticus  major.  The 
tissue  in  which  the  nerve  lies  is  very  dense,  and  the  dissection  in  conse- 
quence is  rendered  somewhat  difficult. 

Rectus  Capitis  Posticus  Major. — This  muscle  springs  by  a 
pointed  origin  from  the  spine  of  the  axis,  and,  expanding  as 
it  passes  upwards  and  outwards,  it  is  inserted  into  the  occipital 
bone  along  the  outer  portion  of  the  inferior  curved  line  and 
the  surface  immediately  below. 

Rectus  Capitis  Posticus  Minor. — This  is  a  minute  fan- 
shaped  muscle,  placed  to  the  inner  side  and  upon  a  deeper 
plane  than  the  preceding  muscle.  It  takes  origin  from  the 
tubercle  on  the  posterior  arch  of  the  atlas,  and  is  inserted 
into  the  inner  part  of  the  inferior  curved  line  of  the  occipital 
bone  and  the  surface  between  this  and  the  foramen  magnum. 

Obliquus  Capitis  Inferior. — This  muscle  stretches  from  the 
bifid  spine  of  the  axis,  from  the  extremity  of  which  it  takes 
origin,  to  the  posterior  tubercle  of  the  transverse  process  of 
the  atlas.  The  great  occipital  nerve  will  be  seen  hooking 
round  its  lower  border. 

Obliquus  Capitus  Superior. — This  small  muscle  springs 
from  the  transverse  process  of  the  atlas,  and  is  inserted  into 
the  occipital  bone  in  the  interval  between  the  curved  lines. 

Posterior  Division  of  the  Sub -Occipital  Nerve.  —  The 
posterior  division  of  the  sub-occipital  nerve  does  not  divide 
into  an  external  and  internal  branch.  It  enters  the  sub- 
occipital triangle  by  passing  backwards  between  the  posterior 
arch  of  the  atlas  and  the  vertebral  artery ;  so  that  even  in 
cases  where  all  its  branches  have  been  divided,  the  trunk  is 
readily  found  in  this  position.  The  nerve  at  once  breaks 
up  into  branches  which  go  to  supply  five  muscles — viz.,  the 
two  recti,  the  two  oblique  muscles,  and  the  complexus.  In 
addition  to  these  muscular  twigs  it  gives  a  communicating,  and 
sometimes  a  cutaneous  filament. 

The  communicating  branch  generally  proceeds  from  the 
nerve    to  the  obliquus   capitis   inferior,   and   joins   the   great 


DORSAL  ASPECT  OF  THE  TRUNK  157 

occipital  nerve.  The  cutaneous  bra?ich  when  present  accom- 
panies the  occipital  artery  to  the  integument  over  the  occiput. 

Vertebral  Artery  (arteria  vertebralis). — It  is  only  a  small 
portion  of  this  vessel  which  occupies  the  sub-occipital  triangle. 
Emerging  from  the  foramen  in  the  transverse  process  of  the 
atlas,  it  runs  backwards  and  inwards  in  the  groove  upon  the 
posterior  arch  of  the  same  bone.  In  this  course  it  crosses 
the  sub-occipital  nerve,  and  lies  immediately  behind  the 
lateral  mass  of  the  atlas.  It  leaves  the  space  and  enters  the 
cranial  cavity  through  the  foramen  magnum  by  turning  for- 
wards below  the  posterior  occipito-atlantal  ligament  and 
piercing  the  dura  mater. 

Small  branches  proceed  from  the  vertebral  artery  in  this 
situation  to  supply  the  parts  in  its  immediate  neighbourhood, 
and  to  anastomose  with  the  arteria  princeps  cervicis  and  the 
arteria  profunda  cervicis. 

Dissection  to  open  the  Spinal  Canal.  —The  first  step  consists  in 
thoroughly  cleaning  the  vertebral  laminae  and  spinous  processes  upon  either 
side.  The  multifidus  spinae  must  also  be  completely  removed  from  the 
back  of  the  sacrum.  At  the  same  time  the  posterior  primary  divisions 
must  be  retained,  so  that  their  continuity  with  the  various  spinal  nerve- 
trunks  may  be  afterwards  established.  The  posterior  wall  of  the  spinal 
canal  should  now  be  removed  in  one  piece  by  sawing  through  the  laminae 
of  the  vertebrae  on  either  side,  and  dividing  the  ligamenta  subflava,  from 
the  third  cervical  vertebra  down  to  the  lower  opening  of  the  canal  on  the 
back  of  the  sacrum. 

In  making  this  dissection  the  student  must  attend  to  the  following 
points: — (1)  the  cut  should  be  directed  through  the  laminae  close  to  the 
inner  side  of  the  articular  processes  ;  (2)  the  saw  must  be  used  in  an  oblique 
plane,  so  that  the  cut  through  the  lamina.1  slants  slightly  inwards  ;  (3)  in 
cutting  through  the  cervical  laminae  the  head  and  neck  should  hang  over 
the  end  of  the  table,  and  be  pressed  as  far  forwards  as  possible  whilst  the 
saw  is  worked  from  below  upwards  ;  (4)  in  the  case  of  the  lumbar  region, 
where,  indeed,  most  difficulty  will  be  met,  a  high  block  must  be  placed 
under  the  abdomen  of  the  subject,  whilst  the  blocks  supporting  the  chest 
and  pelvis  are  removed.  It  will  probably  be  necessary  at  this  point  to 
have  recourse  to  the  hammer  and  chisel. 

The  laminae  and  spinous  processes  which  are  thus  removed  are  connected 
with  each  other  by  the  ligamenta  subflava  and  the  supraspinous  and 
interspinous  ligaments.  They  should  therefore  be  laid  aside  for  the  present. 
A  description  of  these  ligaments  will  be  found  farther  on.  When  the 
specimen  is  fresh,  however,  the  dissector  should  note  the  high  elasticity  of 
the  ligamenta  subflava.     This  can  be  tested  by  stretching  the  specimen. 

Between  the  dura  mater  and  the  walls  of  the  spinal  canal,  ihe  dissector 
will  notice  a  quantity  of  loose  areolar  tissue  and  soft  fat.  The  latter  is 
especially  plentiful  in  the  sacral  region,  where  it  resembles  somewhat  the 
marrow  which  occupies  the  medullary  cavity  of  a  long  bone.  In  the  midst 
of  this  areolo- fatty  material,  great  numbers  of  large  veins  and  minute 
arteries  are  found  ramifying  upon  the  walls  of  the  canal. 


158  HEAD  AND  NECK 

Spinal  Arteries. — A  minute  spinal  artery  in  a  well-injected 
subject  will  be  seen  entering  the  spinal  canal  through  each 
intervertebral  foramen.  These  arteries  are  derived  from 
different  sources  in  the  different  regions  of  the  spine.  In  the 
cervical  region  they  come  from  the  vertebral  artery ;  in  the 
dorsal  region  from  the  dorsal  branches  of  the  intercostal 
arteries  ;  in  the  lumbar  region  from  the  dorsal  branches  of  the 
lumbar  arteries.  They  supply  with  blood  the  spinal  cord  and 
its  meninges,  the  bones,  the  periosteum,  and  the  ligaments  ; 
and  their  arrangement  is  very  much  the  same  in  each  of  the 
three  regions. 

Each  spinal  artery  may  be  looked  upon  as  giving  off  three 
main  twigs :  of  these,  one,  termed  the  pre-laminar  branch, 
a  very  small  twig,  ramifies  upon  the  deep  surface  of  the 
neural  arches  and  ligamenta  subflava ;  another,  the  neural 
branch,  can  be  followed  to  the  dura  mater,  which  it  pierces 
immediately  above  the  point  of  exit  of  the  corresponding 
spinal  nerve;  whilst  the  third,  the  post-central  branch,  is  carried 
inwards  in  front  of  the  dura  mater  towards  the  posterior 
surface  of  the  vertebral  bodies.  The  last-mentioned  branch 
divides  into  an  ascending  and  descending  twig.  These 
anastomose  with  the  corresponding  twigs  of  the  arteries 
above  and  below,  and  in  this  manner  a  continuous  series  of 
minute  arterial  arcades  is  formed.  From  these  arcades, 
branches  pass  inwards  so  as  to  form  a  series  of  cross  anastomoses 
with  the  corresponding  vessels  of  the  opposite  side. 

In  the  cervical  region  small  branches  from  the  ascending 
cervical  artery  also  find  their  way  into  the  spinal  canal ; 
whilst  in  the  sacral  portion  of  the  canal  the  dissector  will  find 
branches  from  the  lateral  sacral  arteries. 

Intraspinal  Veins. — These  are  very  large  and  very  com- 
plicated in  their  arrangement.  They  may  be  looked  upon  as 
forming  a  posterior  and  an  anterior  intraspinal  plexus. 

The  posterior  intraspinal  venous  plexus  consists  of  two  main 
longitudinal  vessels,  united  by  many  cross  branches,  which 
run  along  the  deep  aspect  of  the  neural  arches  and  ligamenta 
subflava.  Above,  they  communicate  with  the  occipital  sinus, 
whilst  all  the  way  down  they  are  connected  with  the  dorsal 
spinal  venous  plexus  by  wide  channels  which  pierce  the 
ligamenta  subflava.  Laterally  they  send  branches  through 
the  intervertebral  foramina  to  join  the  posterior  branches  of 
the  intercostal  and  lumbar  veins. 


DORSAL  ASPECT  OF  THE  TRUNK  159 

The  anterior  intraspinal  venous  plexus  cannot  be  dissected 
whilst  the  spinal  cord  and  its  membranes  are  in  situ,  but  it 
will  be  more  convenient  to  describe  it  at  this  stage.  Indeed, 
the  dissection  is  one  of  considerable  difficulty,  even  under 
the  most  advantageous  circumstances.  Like  the  preceding, 
it  is  composed  of  two  longitudinal  venous  channels  placed 
one  upon  either  side  of  the  posterior  common  ligament  of  the 
vertebral  bodies,  and  joined  by  numerous  transverse  branches 
which  cross  the  mesial  plane  under  cover  of  this  ligament. 
These  transverse  veins  receive  large  tributaries  from  the 
interior  of  the  vertebral  bodies.  Superiorly  each  of  the  main 
longitudinal  channels  communicates  with  the  occipital  and 
basilar  sinuses  within  the  cranium,  and  gives  off  a  branch 
which  emerges  above  the  neural  arch  of  the  atlas  to  form  the 
commencement  of  the  vertebral  vein.  Opposite  the  various 
intervertebral  discs  they  send  off  branches  which  run  towards 
the  intervertebral  foramina,  and,  joining  the  corresponding 
branches  of  the  posterior  intraspinal  plexus,  form  a  plexus 
around  the  corresponding  spinal  nerve. 

Meninges  of  the  Spinal  Cord — Fig.  67. — The  spinal  cord, 
like  the  brain,  with  which  it  is  continuous,  is  enveloped  by 
three  membranes  termed  meninges.  The  most  external 
investment  is  a  strong  fibrous  membrane  called  the  dura 
mater;  the  second,  in  order  from  without  inwards,  is  a  non- 
vascular tunic  termed  the  arachnoid  mater;  whilst  the  third 
and  most  internal  is  the  pia  mater.  These  membranes  are 
directly  continuous  with  the  corresponding  investments  of 
the  brain. 

Dissection. — The  outer  surface  of  the  dura  mater  must  now  be  cleaned. 
This  is  effected  by  removing  from  the  spinal  canal  the  loose  areolar  tissue, 
soft  fat,  and  posterior  intraspinal  veins.  It  is  necessary,  also,  to  carefully 
define  the  numerous  lateral  prolongations  which  the  membrane  gives  to  the 
spinal  nerves. 

Dura  Mater  Spinalis — Fig.  67. — In  the  spinal  canal  the 
dura  mater  constitutes  an  exceedingly  dense  and  tough  fibrous 
tube,  which  extends  from  the  foramen  magnum  above,  to  the 
level  of  the  second  or  third  piece  of  the  sacrum  below.  Even 
before  this  tube  of  membrane  is  laid  open,  the  dissector  can 
readily  satisfy  himself  that  it  is  very  loosely  adapted  to  the 
spinal  cord  and  the  nerve-roots  which  form  the  cauda  equina  ; 
in  other  words,  it  is  very  capacious  in  comparison  with  the 
volume  of  its  contents.      Its  calibre,  moreover,  is  by  no  means 


i6o  HEAD  AND  NECK 

uniform  ;  in  the  cervical  and  lumbar  regions  it  is  considerably 
wider  than  in  the  dorsal  region,  whilst  in  the  sacral  canal  it 
rapidly  contracts  and  finally  ends  by  blending  with  the  filum 
terminate,  a  fibrous  thread  which  is  prolonged  downwards 
through  the  sacral  canal  from  the  extremity  of  the  spinal  cord. 
Above,  the  dura  mater  is  firmly  attached  to  the  third  cervical 
vertebra,  to  the  axis  vertebra,  and  around  the  margin  of  the 
occipital  foramen ;  below,  the  filum  terminale,  on  which  it 
terminates,  can  be  traced  as  far  as  the  dorsal  aspect  of  the 
coccyx,  where  it  is  lost  by  blending  with  the  periosteum 
investing  that  bone. 

If  the  student  recall  the  characteristics  of  the  cranial  dura 
mater,  he  cannot  fail  to  observe  certain  striking  points  of 
difference  between  it  and  the  spinal  dura  mater.  The  relations 
which  the  latter  presents  to  the  walls  of  the  spinal  canal  are 
altogether  different.  Within  the  cranial  cavity  the  dura  mater 
is  closely  adherent  to  the  bones,  and  forms  for  them  an  internal 
periosteum.  As  it  is  traced  into  the  spinal  canal,  however,  it 
splits  at  the  foramen  magnum  into  its  two  constituent  layers. 
The  inner  of  these  two  laminae  is  carried  downwards  as  the 
long  cylindrical  tube  which  encloses  the  spinal  cord.  The 
outer  lamina,  which  is  very  much  thinner,  becomes  continuous, 
behind  and  on  each  side  of  the  foramen  magnum,  with  the 
periosteum  on  the  exterior  of  the  cranium,  whilst  in  front  it  is 
prolonged  downwards  into  the  vertebral  canal  in  connection 
with  the  ligaments  and  periosteum  on  the  anterior  wall  of  the 
canal.  The  spinal  dura  mater  corresponds,  therefore,  to  the 
supporting  layer  of  the  cranial  dura  mater  and  to  it  alone. 
It  is  separated  from  the  walls  of  the  spinal  canal  and  its  lining 
periosteum  by  an  interval  or  space,  which  is  filled  by  loose 
fat,  areolar  tissue,  and  the  intraspinal  plexuses  of  veins.  In 
connexion  with  the  spinal  dura  mater  there  are  no  venous 
sinuses  such  as  are  present  in  the  cranial  cavity,  but  it  should 
be  noted  that  the  intraspinal  veins,  placed  between  the 
periosteum  of  the  spinal  canal  and  the  tube  of  dura  mater, 
occupy  the  same  morphological  plane  as  the  cranial  sinuses. 
Another  feature  which  serves  to  distinguish  the  spinal  dura 
mater  from  the  cranial  dura  mater  consists  in  the  fact  that  it 
gives  off  from  its  deep  surface  no  partitions  or  septa. 

The  cylindrical  tube  of  spinal  dura  mater  does  not  lie 
free  within  the  vertebral  canal,  although  its  attachments  are 
of  such  a  nature  that  they  do  not  in  any  way  interfere  with 


DORSAL  ASPECT  OF  THE  TRUNK 


161 


the  free  movement  of  the  vertebral  column.  On  either  side 
the  spinal  nerve -roots,  as  they  pierce  the  dura  mater,  carry 
with  them  into  the  intervertebral  foramina  tubular  sheaths  of 
the  membrane,  whilst  in  front  loose  fibrous  prolongations — 
more  numerous  above  and  below  than  in  the  dorsal  region — 
connect  the  tube  of  dura  mater  to  the  posterior  common 
ligament  of  the  vertebral   column.       No   connexion    of  any 

Dura  mater 
Arachnoid 

Ligamentum  denticulatum 


Arachnoid 


Posterior  nerve-root 


Spinal  ganglion 


Anterior  division 
of  nerv. 

Posterior  divisiot 
of  nerve 


— — Dura  mater 


Anterior  nerve-root 
(cut) 

Posterior  nerve-root 

Anterior  nerve-root 
(cut) 


Ligamentum 
denticulatum 


Pia  mater 


Anterior  nerve-root 


Fig.  67. — Membranes  of  the  Spinal  Cord,  and  the  mode  of  origin 
of  the  Spinal  Nerves. 

kind  exists  between  the  dura  mater  and  the  neural  arches  ol 
the  vertebrae  or  ligamenta  subflava. 

Dissection. — The  tube  of  dura  mater  may  now  be  opened  with  the 
scissors.  The  incision  should  be  carried  through  the  membrane  in  the 
mesial  plane.  Care,  however,  must  be  taken  not  to  injure  the  delicate 
arachnoid,  which  is  subjacent. 

Subdural  Space  (cavum  subdurale). — The  capillary  interval 
between  the  dura  mater  and  the  arachnoid  mater  is  termed 
the  subdural  space — Fig.  67.  The  deep  surface  of  the  dura, 
which  is  turned  towards  this  space,  is  smooth,  moist,  and 
polished.      Upon   either   side   the    dissector   will    notice    the 

VOL.   II — 11 


1 62  HEAD  AND  NECK 

series  of  apertures  of  exit  for  the  roots  of  the  spinal  nerves. 
These  are  ranged  in  pairs  opposite  each  intervertebral 
foramen.  The  subdural  space  is  prolonged  outwards  for  a 
short  distance  upon  each  of  the  nerve-roots,  and  has  a  free 
communication  with  the  lymph  paths  present  in  these  nerves. 

Viewed  from  the  inside  of  the  tube  of  dura  mater,  each  of  the  two 
nerve-roots  belonging  to  a  spinal  nerve  is  seen  to  carry  with  it  a  special 
and  distinct  sheath.  When  examined,  however,  on  the  outside  of  the  tube 
of  dura  mater,  the  appearance  is  such  that  the  dissector  might  be  led  to 
conclude  that  both  roots  are  enveloped  in  one  sheath.  This  is  due  to  the 
fact  that  the  two  sheaths  are  closely  held  together  on  the  outside  by  inter- 
vening connective  tissue,  which  can  be  removed  with  a  little  careful  dissec- 
tion. When  this  is  done,  the  two  tubular  sheaths  will  be  observed  to 
remain  distinct  as  far  as  the  ganglion  on  the  posterior  root  of  the  nerve. 
At  this  point  they  blend  with  each  other. 

Arachnoidea  Spinalis — Fig.  67. — The  arachnoid  resembles 
the  dura  mater  in  forming  a  loose,  wide  investment  for 
the  spinal  cord.  Unlike  the  dura,  however,  it  is  remark- 
able for  its  great  delicacy  and  transparency.  The  sac  which 
it  forms  is  most  capacious  towards  its  lower  part,  where  it 
envelops  the  extremity  of  the  cord  and  the  collection  of  long 
nerve-roots  which  constitute  the  Cauda  equina.  Here  it  can 
be  most  easily  demonstrated  by  making  an  incision  into  it, 
and  inserting  the  handle  of  the  scalpel,  or,  better  still,  by 
inflating  the  sac  with  air  by  means  of  a  blowpipe.  Above, 
the  arachnoid  mater  becomes  continuous  at  the  level  ot  the 
foramen  magnum  with  the  corresponding  membrane  which 
clothes  the  brain,  whilst,  laterally,  it  is  prolonged  outwards 
upon  the  various  nerve -roots,  thus  contributing  to  each  a 
tubular  sheath. 

Sub-arachnoid  Space  (cavum  subarachnoideale) — Fig.  67. 
— This  term  is  applied  to  the  wide  space  between  the 
arachnoid  and  pia  mater.  It  is  occupied  by  a  variable 
amount  of  cerebro- spinal  fluid,  and  is  directly  continuous 
with  the  cranial  sub -arachnoid  space.  Three  incomplete 
septa  partially  subdivide  the  spinal  sub-arachnoid  space  into 
compartments.  One  of  these  septa  is  a  mesial  partition 
called  the  septuni  posticum,  which  connects  the  pia  mater 
covering  the  posterior  aspect  of  the  cord  with  the  arachnoid 
mater.  In  the  upper  part  of  the  cervical  region  the  septum 
posticum  is  very  imperfect,  and  is  simply  represented  by  a 
number  of  strands  passing  between  the  two  membranes ;  in 
the  lower  part  of  the  cervical  region  and  in  the  dorsal  region 


DORSAL  ASPECT  OF  THE  TRUNK  163 

it   becomes   tolerably  complete.     The   other   two    septa    are 

formed  by  the  ligamenta  denticulata.     These  spread  outwards 

from  each  side  of  the  spinal  cord,  and  will  be  studied  with 

the  pia  mater. 

Dissection. — Clear  away  the  arachnoid  mater  from  a  portion  of  the  cord, 
and  proceed  to  the  study  of  the  pia  mater. 

Pia  Mater  Spinalis. — This  is  a  firm  vascular  membrane, 
which  closely  invests  and  is  firmly  adherent  to  the  surface  of 
the  spinal  cord.  It  is  thicker  and  denser  than  the  corre- 
sponding membrane  which  envelops  the  brain.  This  is 
largely  due  to  the  addition  of  an  outer  fibrous  layer  in  which 
the  fibres  chiefly  run  in  the  longitudinal  direction.  The  pia 
mater  is  firmly  attached  to  the  surface  of  the  spinal  cord, 
and  in  front  it  sends  a  fold  into  the  antero-median  fissure  of 
the  cord.  The  septum  which  occupies  the  postero-median 
fissure  of  the  cord  is  likewise  firmly  attached  to  its  deep 
surface.  Anteriorly,  in  the  mesial  plane,  the  pia  mater  is 
thickened  in  the  form  of  a  longitudinal  glistening  band, 
which  receives  the  name  of  the  linea  sple?ide?is.  Of  course, 
this  can  only  be  seen  after  the  cord  has  been  removed  from 
the  spinal  canal.  The  blood  vessels  of  the  cord  lie  between 
the  two  layers  of  the  pia  mater,  and  the  various  spinal  nerves 
receive  from  it  closely  fitting  sheaths  which  blend  with  their 
connective-tissue  sheaths. 

Ligamentum  Denticulatum — Figs.  67  and  68. — This  is  a 
remarkable  band,  which  stretches  outwards  from  either  side 
of  the  pia  mater,  so  as  to  connect  it  with  the  dura  mater. 
Its  pial  or  inner  attachment  extends  in  a  continuous  line  be- 
tween the  anterior  and  posterior  nerve-roots,  from  the  level  of 
foramen  magnum  above  to  the  level  of  the  body  of  the  first 
lumbar  vertebra  below.  Its  outer  margin  is  widely  serrated  or 
denticulated.  From  twenty  to  twenty-two  denticulations  may 
be  recognised.  They  occur  in  the  intervals  between  the 
spinal  nerves,  and,  pushing  the  arachnoid  before  them,  they 
are  attached  by  their  pointed  extremities  to  the  inner  surface 
of  the  dura  mater. 

The  ligamenta  denticulata  partially  subdivide  the  sub- 
arachnoid space  into  an  anterior  and  a  posterior  compart- 
ment. In  the  anterior  compartment  the  anterior  nerve-roots 
pass  outwards ;  the  posterior  compartment  contains  the 
posterior  nerve-roots,  and  is  imperfectly  subdivided  into  two 
lateral  subdivisions  by  the  septum  posticum. 

n  —  ll  a 


164 


HEAD  AND  NECK 


By  means  of  the  ligamentum  denticulatum  of  either  side, 
the  spinal  cord  is  suspended  in  the  middle  of  the  sac  of  dura 
mater. 

Spinal  Cord  (medulla  spinalis). — The  spinal  cord  itself 
may  now  be  studied  in  situ.  It  is  a  cylindrical  structure, 
slightly  flattened  in  front  and  behind,  which  extends  from 
the  margin  of  the  foramen  magnum,  where  it  is  continuous 
with  the  medulla  oblongata  of  the  brain,  to  the  lower  border 
of  the  body  of  the  first  or  the  upper  border  of  the  body  of 
the  second  lumbar  vertebra.     Its  lower  end  rapidly  tapers  to 

a  point,  and  is  termed 
the  conns  medullaris. 
From  the  extremity  of 
this,  a  slender  filament, 
termed   the  filuni   ter- 


Ligamentum 
denticulatum 


?ninale  or  central  liga- 


FlG.  68. — Lateral  view  of  the  Spinal  Cord, 
Dura  Mater,  and  Ligamentum  Denticula- 
tum.    (Hirschfeld  and  Leveilte. ) 


ment,      is      prolonged 
downwards. 

In  the  female  the 
average  length  of  the 
spinal  cord  is  43  cm.  ; 
in  the  male  it  is  45 
cm. 

Throughout  the 
greater  part  of  the 
dorsal  region  the  spinal 
cord  presents  a  uniform 
girth,  but  in  the  cervical  and  lower  dorsal  regions  it  shows 
marked  swellings,  termed  respectively  the  cervical  and  lumbar 
enlargements.  From  these  expansions  proceed  the  nerves 
which  supply  the  upper  and  lower  limbs.  The  cervical 
swelling  (intumescentia  cervicalis)  is  the  more  evident  of  the 
two.  It  begins  at  the  upper  end  of  the  cord  and  attains 
its  greatest  breadth  (13  to  14  mm.)  opposite  the  fifth  or 
sixth  cervical  vertebra.  Below,  it  subsides  opposite  the 
second  dorsal  vertebra.  The  Iwnbar  swelling  (intumescentia 
lumbalis)  begins  at  the  level  of  the  tenth  dorsal  vertebra, 
and  attains  its  maximum  transverse  diameter  (n  to  13  mm.) 
opposite  the  last  dorsal  vertebra.  Below,  it  rapidly  tapers 
into  the  tapering  conus  medullaris. 

Filum  Terminate. — This  delicate  thread-like  filament  lies 
amidst  the  numerous  long  nerve-roots  which  occupy  the  lower 


DORSAL  ASPECT  OF  THE  TRUNK 


165 


L.V.I. 


Conus 
medullaris 


part  of  the  spinal  canal,  and  it  can  readily  be  detected  from 
these  (1)  by  its  silvery  glistening  appearance,  and  (2)  by  its 
continuity  with  the  extremity  of  the  conus  medullaris. 

Although  the  central  canal  of  the  spinal  cord  is  prolonged 
down  in  its  interior  for  nearly  half  its  length,  and  nervous 
elements  can  be 
traced  in  its  sub- 
stance for  a  like 
distance,  the  filum 
terminale  is  chiefly 
composed  of  pia 
mater  carried  down- 
wards from  the 
conus  medullaris. 
The  linea  splendens 
and  the  lower  ends 
of  the  ligamenta 
denticulata  may  also 
be  considered  to  be 
continued  into  it. 
At  the  level  of  the 
second  or  third 
sacral  vertebra  it 
pierces  the  tapered 
end  of  the  tube  of 
dura  mater,  and  re- 
ceives an  invest- 
ment from  it,  and, 
finally,  reaching  the 
lower  end  of  the 
sacral  canal,  it  ter- 
minates byblending 
with  the  periosteum 
on  the  back  of  the 
coccyx  or  last  piece 
of  the  sacrum. 

In  length  the  filum  terminale  measures  about  six  inches. 
The  part  within  the  tube  of  dura  mater  is  termed  the  filum 
terminale  internum,  the  portion  outside  is  distinguished  as  the 
filum  termi?iale  externum. 

Spinal  Nerves. — Thirty-one  spinal  nerves  take  origin  from 
each  side  of  the  spinal  cord.     These  are  classified  into  five 


S.V.I. 


Fig.  69. 


Coccyx 


-Sagittal  section  through  the  lower  part 
of  the  Vertebral  Canal. 


1 66  HEAD  AND  NECK 

groups,  according  to  the  vertebrae  with  which  they  are  associ- 
ated. The  dorsal,  lumbar,  and  sacral  nerves  correspond  in 
number  with  the  number  of  vertebrae  in  each  of  these  regions, 
— thus,  there  are  twelve  dorsal,  five  lumbar,  and  five  sacral 
nerves,  each  of  which  issues  from  the  spinal  canal  below  the 
vertebra  with  which  it  numerically  corresponds.  In  the 
cervical  region,  however,  there  are  eight  nerves,  the  first  of 
which  comes  out  between  the  occiput  and  the  atlas,  and  is 
therefore  distinguished  by  the  special  name  of  the  sub-occipital 
fierue.     There  is  only  one  coccygeal  nerve  on  each  side. 

Spinal  Nerve-Roots — Figs.  67  and  70. — Each  spinal  nerve 
springs  from  the  side  of  the  spinal  cord  by  two  roots — an  anterior 
(radix  anterior)  and  a  posterior  (radix  posterior).  Except  in 
the  case  of  the  sub-occipital  nerve  (where,  indeed,  the  posterior 
root  is  sometimes  absent),  the  posterior  nerve-root  is  the  larger 
of  the  two.  In  addition  to  this,  the  posterior  root  is  distin- 
guished by  possessing  an  oval  ganglion,  termed  the  spinal 
root-ganglion  (ganglion  spinale).  There  is,  likewise,  a  wide 
physiological  difference  between  the  two  roots, — the  posterior 
root  is  composed  of  afferent  fibres,  the  anterior  root  consists 
of  efferent  fibres.  Immediately  beyond  the  ganglion  the 
two  roots  unite  to  form  the  spinal  nerve-trunk,  which,  in  con- 
sequence, contains  a  mixture  of  both  efferent  and  afferent 
nerve-fibres. 

The  mode  of  attachment  of  the  two  nerve-roots  to  the  side 
of  the  spinal  cord  is  somewhat  different  in  the  two  cases. 
In  each  instance  they  are  attached  by  several  separate  fasci- 
culi (fila  radicularia),  which  spread  out  from  each  other  as 
they  approach  the  cord.  In  the  case  of  the  posterior  root 
these  enter  the  cord  consecutively  along  a  continuous  straight 
line  and  at  the  bottom  of  a  slight  furrow.  The  fasciculi  of 
the  anterior  root,  on  the  other  hand,  are  not  so  regularly 
placed.  They  emerge  from  the  cord  over  an  area  of  some 
breadth.  The  portion  of  the  spinal  cord  which  stands  in 
connection  with  a  pair  of  nerves  receives  the  name  of  a 
"segment  of  the  cord." 

The  size  of  the  nerve-roots  will  be  observed  to  differ  greatly. 
The  lower  lumbar  and  upper  sacral  nerve-roots  are  much 
the  largest,  whilst  the  lower  sacral  and  the  coccygeal  roots 
are  the  smallest.  In  the  cervical  region  the  roots  increase  in 
size  from  above  downwards,  but  more  rapidly  in  the  lower 
members  of  the  group ;  in  the  dorsal  region  the  roots  of  the 


DORSAL  ASPECT  OF  THE  TRUNK 


167 


first  nerve  are  large,  but  those  which  succeed  it  are  small  and 
of  uniform  size. 

In  relative  length,  and  in  the  direction  which  they  follow  in 
the  spinal  canal,  the  nerve-roots  also  show  great  differences. 
This  is  due  to  the  spinal  cord  being  so  much  shorter  than 
the  canal  in  which  it  lies.  In  the  upper  part  of  the  cervical 
region  the  nerve-roots  are  short,  and  proceed  outwards  in  a 
more  or  less  horizontal  direction.  Below  this  the  nerve-roots 
gradually  lengthen,  and  have  to  descend  in  the  spinal  canal 
for  a  distance  which  is  always  increasing  the  farther  down  we 
go.  The  arrangement  of  the  lower  dorsal,  the  lumbar,  sacral, 
and  coccygeal  nerve-roots  is  particularly  characteristic.      They 


Fig.  70.  — A  segment  of  the  spinal  cord  ;  anterior  aspect. 
(Schwalbe,  after  Allen  Thomson. ) 


1.  Anterior  median  fissure. 

2.  Posterior  median  fissure. 

3  and  5.   Fasciculi  of  anterior  nerve-root. 
4.   Postero-lateral  groove. 


6.  Posterior  nerve-root. 
6'.  Spinal  ganglion. 

7.  Anterior  primary  division. 
7'.  Posterior  primary  division. 


are  exceedingly  long,  and  descend  vertically  from  the  lower 
portion  of  the  cord,  in  the  form  of  a  bunch  or  leash  which, 
from  its  appearance,  has  been  termed  the  cauda  equina. 

Mode  of  Exit  of  Spinal  Nerves  from  Spinal  Canal. — The 
six  lower  cervical  nerves,  the  dorsal  nerves,  and  the  lumbar 
nerves  make  their  exit  through  the  intervertebral  foramina ; 
whilst  the  two  divisions  of  each  of  the  upper  four  sacral  nerves 
find  their  way  out  by  the  sacral  foramina.  The  two  upper 
cervical  nerves,  the  fifth  sacral  nerve,  and  the  coccygeal 
nerve,  however,  follow  a  different  course.  The  sub-occipital 
emerges  by  passing  over  the  neural  arch  of  the  atlas,  and  the 
second  cervical  nerve  by  passing  over  the  neural  arch  of  the 
axis.  The  fifth  sacral  and  the  coccygeal  nerve  leave  the 
sacral  canal  through  its  lower  aperture  (Fig.  71). 


i68 


HEAD  AND  NECK 


Dissection.  —  The  nerve-roots  of  one  or  two  spinal  nerves  in  each 
region  should  be  followed  into  the  corresponding  intervertebral  foramina. 
This  can  be  easily  done  by  snipping  away  the  articular  processes  with  the 
bone-pliers.  The  position  of  the  ganglion  on  the  posterior  root,  the 
connections  of  the  sheath  of  dura  mater,  the  union  of  the  two  roots  to  form 
the  spinal  nerve-trunk,  and  the  division  of  the  latter    into  the  anterior 

Filum  trrminale 

Cauda  equina 
Dura  mater 


Filum 

terminale 

Fifth  sacral  nerve 


Coccygeal  nerve 


Fig.  71. — Sacral  Canal  opened  up  from  behind  to  show  the  Sacral 
Xerve-roots  (lower  part  of  Cauda  Equina)  and  the  Membranes 
in  relation  to  them.      (After  Testut. ) 

and  posterior  primary  divisions,  can  thus  be  studied.  An  attempt  should 
also  be  made  at  the  same  time  to  discover  the  minute  ramus  meningeus. 
This  is  a  fine  twig  which  is  formed  by  the  union  of  a  small  filament  from 
the  spinal  nerve-trunk  with  a  minute  branch  from  the  sympathetic  cord. 
It  takes  a  recurrent  course  through  the  intervertebral  foramen  to  end  in 
the  bones  and  periosteum  of  the  vertebral  canal. 

Spinal  Root-Ganglia. — These  ganglia  are  oval  swellings 
developed  upon  the  posterior  nerve-roots,  just  before  they 
unite  with  the  anterior  roots  to  form  the  spinal  nerve-trunks. 


DORSAL  ASPECT  OF  THE  TRUNK  169 

They  are  usually  found  upon  the  posterior  roots  of  all  the 
nerves,  although  occasionally  the  ganglion  may  be  absent  in 
the  case  of  the  sub-occipital  nerve. 

Except  in  the  case  of  the  two  upper  cervical  nerves, 
and  the  sacral  and  coccygeal  nerves,  the  spinal  ganglia  are 
formed  upon  the  posterior  nerve-roots  as  they  lie  in  the 
intervertebral  foramina.  The  ganglia  of  the  first  two 
cervical  nerves  lie  upon  the  neural  arches  of  the  first  and 
second  cervical  vertebrae  respectively ;  the  ganglia  of  the 
sacral  nerves  are  placed  within  the  sacral  canal,  but  out- 
side the  tube  of  dura  mater.  The  ganglion  on  the  posterior 
root  of  the  coccygeal  nerve  will  be  found  inside  the  tube 
of  dura  mater. 

Spinal  Nerve -Trunks. — These  are  formed  by  the  union 
of  the  anterior  and  posterior  nerve-roots  immediately  beyond 
the  spinal  ganglia,  and  from  what  has  been  said  it  must 
be  evident  that  this  union  takes  place  in  the  case  of  the 
coccygeal  and  sacral  nerves  in  the  sacral  canal ;  in  the 
lumbar,  dorsal,  and  lower  six  cervical  nerves,  in  the  inter- 
vertebral foramina \  and  in  the  case  of  the  first  two  cervical 
nerves,  on  the  neural  arches  of  the  atlas  and  axis. 

The  nerve-trunk  is  exceedingly  short ;  indeed,  it  almost 
immediately  divides  into  its  anterior  and  posterior  primary 
divisions.  In  the  case  of  the  sacral  and  coccygeal  nerves, 
this  subdivision  takes  place  in  the  sacral  canal,  and  the 
spinal  nerve-trunks  of  these  nerves  are  distinctly  longer  than 
in  the  case  of  the  nerves  which  occupy  a  higher  level. 

The  distribution  of  the  posterior  primary  divisions  has 
already  been  examined  (p.  148). 

Dissection. — At  this  stage  the  dissector  may  adopt  one  of  two  methods 
in  the  further  treatment  of  the  cord  and  the  nerves  which  spring  from  it. 
If  the  cord  is  fresh  and  in  such  a  condition  that  it  may  be  successfully 
hardened,  it  is  best  to  transfer  it  at  once  to  the  preservative  fluid.  If,  on  the 
other  hand,  it  is  soft  and  not  fit  for  proper  preservation,  it  should  be  removed 
with  all  its  membranes  and  nerve-roots,  and  placed  in  a  cork-lined  tray 
filled  with  water.  There  is  no  method  by  which  the  arachnoid,  the  pia 
mater,  the  ligamenta  denticulata,  and  the  nerve-roots  can  be  so  well 
studied  as  this. 

In  removing  the  spinal  cord,  the  spinal  nerves  should  be  divided  as 
they  lie  in  the  intervertebral  foramina,  and  in  such  a  manner  that  as 
long  a  piece  as  possible  of  each  nerve  remains  attached  to  the  dura 
mater  and  the  cord.  Wherever  it  is  possible  the  ganglia  should  be 
taken  with  the  nerves.  The  same  rule  also  applies  to  the  sacral  nerves. 
The  cord  and  its  membranes  should  then  be  cut  across  at  the  highest 
limit  of  the  vertebral  dissection.  By  pulling  upon  the  dura  mater  the 
whole  specimen   may  now  be  lifted  from   the  vertebral  canal  and  trans- 


i7o  HEAD  AND  NECK 

ferred  to  the  water-bath.  The  dura  mater  should  then  be  slit  down 
the  mesial  plane  over  the  front  of  the  cord,  and  the  edges  of  each 
lateral  piece  drawn  outwards.  By  fixing  the  dura  mater  to  the  cork  at 
the  bottom  of  the  tray  with  pins,  the  further  dissection  can  be  conducted 
with  great  advantage. 

Arteries  of  the  Spinal  Cord. — It  is  only  in  cases  where 
a  paint  or  a  starch  injection  has  been  used  that  the  spinal 
arteries  can  be  made  out  satisfactorily. 

A  large  number  of  small  arteries  are  supplied  to  the 
spinal  cord.  These  are  the  a?iterior  and  posterior  spinal 
arteries  which  spring  from  the  vertebral,  and  a  series  of 
lateral  spinal  or  neural  arteries  which  reach  the  side  of  the 
spinal  cord  and  are  derived  from  different  sources  in  each 
region.  In  the  ?ieck  they  come  from  the  spinal  branches  of 
the  vertebral,  ascending  cervical,  and  deep  cervical  arteries ; 
and  in  the  dorsal  and  lumbar  regions  from  the  spinal  twigs  of 
the  dorsal  branches  of  the  intercostal  and  lumbar  arteries. 
By  the  anastomoses  of  these  arterial  twigs,  five  longitudinal 
trunks  are  formed  upon  the  surface  of  the  spinal  cord. 
One  of  these  occupies  the  mesial  plane  in  front,  and  may 
be  termed  the  anteromedian  artery.  The  other  four  are 
placed  in  relation  to  the  sulci  along  which  the  posterior 
nerve-roots  enter  the  cord.  One  runs  downwards  in  front 
of  the  line  of  entrance  of  these  roots,  and  the  other  behind 
it  on  each  side  of  the  cord.  These  slender  arterial  trunks 
may  therefore  be  termed  the  postero- lateral  longitudinal 
vessels. 

The  ant ero -median  vessel  is  formed  in  its  upper  part  by  the  union 
of  the  two  anterior  spinal  branches  of  the  vertebral  arteries.  One  of 
these  is  larger  than  the  other,  and  takes  a  much  greater  share  in  the 
formation  of  the  median  trunk.  Below  the  level  of  the  fifth  pair  of 
cervical  nerves  the  continuity  of  the  median  vessel  depends  upon  the 
reinforcements  which  it  obtains  from  the  lateral  spinal  vessels.  The 
number  of  lateral  spinal  arteries  which  join  the  median  vessel  is  very 
variable.  The  majority  of  these  arteries  end  on  the  nerve-roots ;  five 
to  ten  only  reach  the  median  vessel.  The  antero-median  artery  runs 
downwards,  under  cover  of  the  linea  splendens  of  the  pia  mater.  Its 
calibre  is  uniform  throughout,  and  where  the  cord  ends  it  proceeds 
onwards  for  some  distance  upon  the  filum  terminale. 

The  post  ero- lateral  arteries  on  each  side  of  the  cord  are  formed  in 
the  upper  part  of  the  cervical  region  by  the  bifurcation  of  the  corre- 
sponding posterior  spinal  branch  of  the  vertebral  artery.  Lower  down 
their  continuity  is  maintained  by  twigs  which  reach  them  on  the  posterior 
roots  of  the  spinal  nerves  from  the  lateral  spinal  arteries.  It  may  be 
regarded  as  a  rule,  that  where  a  lateral  spinal  artery  gives  a  branch  to 
one  of  the  postero-lateral  arterial  trunks,  it  does  not  furnish  another 
to  the  antero-median  arterial  trunk.     In  this  way  different  lateral  spinal 


DORSAL  ASPECT  OF  THE  TRUNK  171 

arteries  are  in  connexion  with  the  longitudinal  trunks  on  the  anterior 
and  posterior  aspects  of  the  cord.  The  postero-lateral  vessels  end  at  the 
lower  extremity  of  the  cord. 

From  the  five  main  arterial  channels  which  thus  extend  along  the  cord 
numerous  anastomosing  twigs  ramify  in  the  pia  mater. 

Veins  of  the  Spinal  Cord. — These  veins  are  small  and 
numerous,  and  their  disposition  cannot  be  said  to  correspond 
with  that  of  the  arteries.  They  are  very  tortuous,  and  form 
a  plexus  with  elongated  meshes.  Six  more  or  less  perfect 
longitudinal  venous  trunks  may  be  noticed  on  the  surface  of 
the  cord  in  connection  with  this  plexus.  Two  of  these  are 
mesial,  and  are  placed  respectively  on  the  anterior  and 
posterior  aspects  of  the  cord.  The  anterior  trunk  runs 
upwards  under  cover  of  the  antero- median  spinal  artery. 
The  other  four  are  lateral,  and  are  situated  two  on  either 
side  of  the  cord  in  relation  respectively  to  the  anterior  and 
posterior  nerve-roots. 

Upon  either  side,  the  veins  of  the  spinal  cord  effect 
communications  with  the  veins  in  the  spinal  canal  by  means 
of  small  twigs  which  run  outwards  on  the  nerve-roots. 

How  to  distinguish  the  anterior  from  the  posterior  surface  of 
the  spinal  cord. 


Anterior  Surface. 
Linea  splendens. 

Single  anterior  spinal  artery  in 
mesial  plane. 

Anterior  nerve  -  roots  smaller 
than  posterior,  and  springing 
by  fasciculi  which  emerge  from 


Posterior  Surface. 

The  postero-lateral  arteries  in 
relation  to  the  posterior  nerve- 
roots. 

Fasciculi  of  origin  of  posterior 
nerve-roots  entering  the  cord 
along  a  straight  and  continu- 
ous line,  and  at  the  bottom  of 
a  distinct  sulcus. 


the  cord,  not  in  a  continuous   ;    3.    Posterior  nerve-roots  larger  than 
straight    line,    but    irregularly  the  anterior,  and  provided  with 

over  an  area  of  some  width.  ganglia. 

Preservation  of  the  Spinal  Cord. — If  the  spinal  cord  be  in  a  fit  state 
for  preservation,  the  dissector  should  immerse  it  for  a  few  weeks  in  methyl- 
ated spirit,  to  which  a  small  amount  (4  per  cent)  of  formalin  has  been 
added.  When  sufficiently  firm,  the  dissector  should  endeavour  to  learn 
something  of  its  internal  structure  by  making  transverse  sections  through 
it  at  different  levels,  and  inspecting  the  cut  surface  closely  with  the  naked 
eye,  or  with  the  aid  of  a  magnifying  glass. 

Internal  Structure  of  the  Spinal  Cord. — A  good  deal  can 
be  learned  by  a  naked-eye  inspection  of  cross  sections  of  the 
cord  made  in  different  regions  and  at  different  levels. 

The  spinal  cord  is  then  seen  to  be  a  bilateral  structure. 


172 


HEAD  AND  NECK 


It  is  partially  subdivided  into  a  right  and  a  left  half  by  two 
median  clefts, — one  upon  the  anterior,  and  the  other  upon 
the  posterior  aspect.  These  clefts  are  called  the  antero- 
media?i  and  the  posteromedian  fissures,  and  they  extend  along 
the  entire  length  of  the  cord. 

At  the  same  time,  it  must  be  noted  that  these  two  median 
fissures  present  many  points  of  difference.  The  antero-median 
fissure  is,  for  the  greater  part  of  its  length,  much  shallower 
than  the  postero-median  fissure ;  further,  it  is  wider  and  much 
more  apparent,  and  the  pia  mater  dips  down  into  it  to  form 
a  fold  or  reduplication  within   it.      The  postero-median   cleft, 

Postero-mesial  column 
Posterior  column  /Postero-lateral  column 


Entering  posterior 
nerve-root 


Formatio  reticularis 

Lateral  column 

Central  canal 

Spinal  accessory  root 

Anterior  horn  of 
grey  matter 


Posterior  horn  of 
grey  matter 


Spinal  accessory  root 


—  Anterior  nerve-root 


Anterior  column 


Fig.  72. — Transverse  section  through  the  upper  part  of  the 
Cervical  Region  of  the  Cord. 

in  addition  to  its  being  deeper  and  narrower,  contains  only  a 
single  septum  of  neuroglia. 

The  two  halves  of  the  cord  thus  marked  off  from  each 
other  are  to  all  intents  and  purposes  symmetrical,  and  they 
are  joined  by  a  more  or  less  broad  band  or  commissure  which 
intervenes  between  the  two  median  fissures. 

An  inspection  of  the  surface  of  each  lateral  half  of  the 
cord  brings  into  view  a  groove  or  furrow  at  some  little  distance 
from  the  postero-median  furrow.  Along  the  bottom  of  this 
groove  the  fasciculi  of  the  posterior  nerve-roots  enter  the 
cord  in  accurate  linear  order.  It  is  called  the  postero-lateral 
sulcus.  There  is  no  corresponding  furrow  on  the  fore-part  of 
each  lateral  half  of  the  cord  in  connection  with  the  emergence 
of  the   fasciculi   of   the    anterior   nerve -roots.     As   we   have 


DORSAL  ASPECT  OF  THE  TRUNK  173 

already  observed,  these  fascicles  emerge  over  a  broad  area, 
which  corresponds  in  its  width  to  the  thickness  of  the  sub- 
jacent extremity  of  the  anterior  horn  of  grey  matter. 

By  means  of  the  postero-lateral  sulcus  and  line  of  entrance 
of  the  fascicles  of  the  posterior  nerve-roots  on  the  one  hand, 
and  the  emergence  of  the  fascicles  of  the  anterior  nerve-roots 
on  the  other  hand,  the  surface  of  each  lateral  half  of  the  cord 
is  subdivided  into  three  columns,  which  are  respectively 
termed  posterior,  lateral,  and  anterior.  The  posterior  column 
(funiculus  posterior)  is  placed  between  the  postero-median 
fissure  and  the  postero-lateral  furrow;  the  lateral  colum?i 
(funiculus  lateralis)  lies  between  the  postero-lateral  furrow  and 
the  outermost  of  the  fascicles  of  the  anterior  nerve-roots  as 
they  emerge  from  the  cord ;  the  anterior  colmnn  (funiculus 
anterior)  includes  that  district  which  extends  from  the  antero- 
median fissure  to  the  emergence  of  the  outermost  of  the 
anterior  nerve-root  fascicles. 

The  spinal  cord  is  composed  of  an  inside  core  of  grey 
matter  which  is  surrounded  on  all  sides  by  an  external  coating 
of  white  matter. 

Grey  Matter  of  the  Spinal  Cord. — The  grey  matter  in  the 
interior  of  the  spinal  cord  has  the  form  of  a  fluted  column. 
When  seen  in  transverse  section,  it  presents  the  shape  of  the 
letter  H-  In  each  lateral  half  of  the  spinal  cord  there  is  a 
crescentic  mass  shaped  somewhat  like  a  comma,  the  con- 
cavity of  which  is  directed  outwards,  and  the  convexity 
inwards.  The  two  crescents  of  opposite  sides  are  connected 
across  the  middle  line  by  a  transverse  band,  which  is  called 
the  grey  commissure.  The  postero-median  fissure  cuts  through 
the  cord  until  it  reaches  the-  grey  commissure.  The  bottom 
of  the  antero-median  fissure  is  separated  from  it  by  an  inter- 
vening strip  of  white  matter  which  is  termed  the  anterior  white 
commissure  (commissura  anterior  alba).  In  the  grey  com- 
missure may  be  seen  the  central  canal  of  the  cord  (canalis 
centralis).  It  is  just  visible  to  the  naked  eye  as  a  minute 
speck.  This  canal  tunnels  the  entire  length  of  the  cord,  and 
opens  above  (after  having  traversed  the  lower  half  of  the 
medulla  oblongata)  into  the  fourth  ventricle  of  the  brain. 
The  portion  of  the  grey  commissure  which  lies   behind  the 

itral  canal  is  called  the  posterior  grey  commissure  (commissura 
posterior);  the  portion  in  front  receives  the  name  of  anterior 
grey  commissure  (commissura  grisea  anterior). 


174  HEAD  AND  NECK 

In  each  crescentic  mass  of  grey  matter  certain  well-defined 
parts  may  be  recognised.  The  projecting  portions  which 
extend  behind  and  in  front  of  the  connecting  transverse  grey 
commissure  are  termed  respectively  the  posterior  and  the 
anterior  cornna  of  grey  matter  (columnae  grisese).  These  can 
be  distinguished  from  each  other  at  a  glance. 

The  a?iterior  cornu  is  short,  thick,  and  very  blunt  at  its 
extremity.  Further,  its  extremity  falls  short  of  the  surface  of 
the  cord,  and  is  separated  from  it  by  a  tolerably  thick  coating 
of  white  matter.  Through  this  the  fascicles  of  the  anterior 
nerve-roots  pass  on  their  way  to  the  surface.  The  thickened 
end  of  the  anterior  cornu  is  termed  the  caput  cornu,  whilst  the 
slightly  constricted  part  close  to  the  grey  commissure  is  called 
the  cervix  cornu.  The  posterior  cornu  is  in  most  localities  in 
the  cord  elongated  and  narrow.  Further,  it  is  drawn  out  to 
a  fine  point  which  almost  reaches  the  bottom  of  the  postero- 
lateral sulcus.  This  pointed  extremity  receives  the  name  of 
the  apex  cornu ;  the  slightly  swollen  part  which  succeeds  it  is 
the  caput  cornu ;  whilst  the  slightly  constricted  part  adjoining 
the  grey  commissure  goes  under  the  name  of  the  cervix  cornu. 

Covering  the  tip  of  the  posterior  cornu  there  is  a  substance 
which  differs  in  its  composition  from  the  general  mass  of  grey 
matter,  and  presents  a  translucent  appearance.  It  is  termed 
the  substantia  gelatinosa  of  Rolando. 

When  we  apply  the  terms  cervical,  dorsal,  lumbar,  sacral,  etc.,  to 
different  portions  of  the  cord,  we  refer  to  those  parts  of  the  cord  to  which 
the  different  groups  of  nerves  are  attached. 

The  grey  matter  is  not  present  in  equal  quantity  through- 
out the  entire  length  of  the  cord.  It  may  be  regarded  as  a 
general  law  that  wherever  there  is  an  increase  in  the  size  of 
the  nerves  attached  to  a  particular  part  of  the  cord,  there  a 
corresponding  increase  of  the  grey  matter  may  be  noticed. 
It  follows  from  this  that  the  districts  in  which  the  grey 
matter  bulks  most  largely  are  the  lumbar  and  cervical 
swellings.  The  great  nerves  which  go  to  form  the  limb 
plexuses  enter  and  pass  out  from  those  portions  of  the  cord. 
In  the  intermediate  dorsal  region  there  is  a  reduction  in  the 
quantity  of  grey  matter  in  correspondence  with  the  smaller 
size  of  the  dorsal  nerves. 

But  the  shape  of  the  crescentic  masses  of  grey  matter  is 
not  the  same  in  all  regions.  In  the  dorsal  region  both  horns 
are  narrow,  although  the  distinction  between  the  anterior  horn 


DORSAL  ASPECT  OF  THE  TRUNK 


*75 


B 


and  the  more  at- 
tenuated posterior 
horn  is  still  suffici- 
ently manifest.  In 
the  cervical  region 
the  contrast  be- 
tween the  cornua 
is  most  marked ; 
the  anterior  horn  is 
very  thick  in  com- 
parison with  the 
much  narrower 
posterior  horn.  In 
the  lumbar  region, 
on  the  other  hand, 
the  difference  in 
the  thickness  of  the 
two  horns  is  not 
nearly  so  apparent 
owing  to  a  broad- 
ening out  of  the 
posterior  horn.  A 
section  taken  from 
the  centre  of  each 
of  these  regions 
can  very  readily 
be  recognised  by 
these  features. 

In  the  dorsal 
region  of  the  cord, 
more  especially  in 
the  upper  part, 
there  is  another 
character  which  is 
very  distinctive.  A 
pointed  and  pro- 
minent triangular 
projection  juts  out 
from  the  external 
aspect  of  the  cres- 
centic  mass  of  grey 
matter  nearly  opposite 


Postero-median  fissure 
Para-median  septum 
Column  of  Goll 

Column  of  Burdach 
Substantia  Rolandi 

Lateral  column 


Central  canal 

Anterior  horn 

Grey  commissure 
Antero-median  fissure 
Fascicles  of  anterior 
nerve-root 
Anterior  column 

Postero-median 
septum 


Substantia  Rolandi 

Posterior  vesicular 
column 


Lateral  horn 
Anterior  horn 
Antero-median  fissure 


— Postero-median  septum 
Entering  posterior 
nerve-root 

_\  Posterior  vesicular 
column 

Lateral  horn 

Antero-median 
fissure 


Postero-median 
fissure 


Fig 


Antero-median 
fissure 


73. — Transverse  sections  through  the  Cord  in 
different  regions.  A.  Cervical  Region  ;  B. 
Mid -dorsal  Region  ;  C.  Lower  Dorsal  Region  ; 
D.   Lumbar  Region. 

the  grey  commissure.      This  is  called 


176 


HEAD   AND  NECK 


the  lateral  horn  (Fig.  73,  B  and  C).  It  disappears  in  the 
region  of  the  cervical  and  lumbar  swellings,  but,  curiously 
enough,  it  again  becomes  evident  both  in  the  upper  cervical 
and  in  the  lower  sacral  regions  of  the  cord. 

Below  the  dorsal  region  of  the  cord  the  postero-median 
cleft  becomes  gradually  shallower  and  the  antero-median 
cleft  deeper,  until  in  the  sacral  region  they  are  found  to 
present  a  very  nearly  equal  depth.  The  central  canal,  in 
correspondence  with  this  change,  comes  to  occupy  the  centre 
of  the  cord  in  its  lower  part. 

White  Matter  of  the  Spinal  Cord. — The  white  matter 
forms  a  thick  coating  on  the  outside  of  the  fluted  column  of 

Tract  of  Goll 


Postero-median  fissure 
Postero-lateral  groove 


Crossed  pyramidal_ 
tract 


Direct  pyramidal  tract 


IYact  of  Burdach 

_    Substantia  gelatinosa 
Rolandi 


Direct  cerebellar 
tract 

Fascicle  of  origin  of 
the  spinal  accessory 
nerve 


\ntero-median  furrow 


FlG.  74. — Transverse  section  through  the  upper  cervical  part  of  the 
Cord  of  a  full-time  Foetus  treated  by  the  Pal-Weigert  process. 

grey  matter.  It  is  marked  off  into  three  columns  (funiculi 
medullar  spinalis).  The  posterior  column  is  wedge-shaped  in 
transverse  section,  and  lies  between  the  postero-median 
fissure  and  the  posterior  cornu  of  grey  matter.  The  lateral 
column  occupies  the  concavity  of  the  grey  crescent.  Behind, 
it  is  bounded  by  the  posterior  grey  cornu  and  the  postero- 
lateral sulcus,  whilst  in  front  it  extends  as  far  as  the  outer- 
most fasciculi  of  the  anterior  nerve -roots  as  they  pass  out 
from  the  anterior  grey  horn.  The  anterior  column  includes 
the  white  matter  between  the  antero-median  fissure  and  the 
anterior  horn  of  grey  matter,  and  also  the  white  matter  which 
separates  the  thick  extremity  of  the  anterior  grey  cornu  from 
the  surface  of  the  cord.  This  latter  portion  of  the  anterior 
column  is  traversed  by  the  emerging  fascicles  of  the  anterior 
nerve-roots. 


DORSAL  ASPECT  OF  THE  TRUNK  177 

In  the  cervical  region  a  faint  longitudinal  groove  runs 
downwards  on  the  surface  of  the  posterior  column  of  the 
cord.  This  indicates  the  position  of  a  septum  which  passes 
into  the  column  from  the  deep  surface  of  the  pia  mater  and 
divides  it  incompletely  into  two  unequal  Strands.  The 
groove  is  termed  the  paramedian  furrow ;  the  smaller  and 
more  internal  of  the  two  strands  is  called  the  postero-median 
column  or  the  tract  of  Go//,  whilst  the  outer  and  larger  strand 
receives  the  name  of  the  postero-externa/  column  or  the  tract 
of  Burdach. 

The  white  matter  of  the  spinal  cord  increases  steadily  in 
quantity  from  below  upwards. 

The  tracts  of  Goll  and  Burdach,  which  form  the  posterior  column  of 
the  cord,  are  composed  of  fibres  which  enter  the  cord  through  the  fascicles 
of  the  posterior  nerve-roots.  In  the  lower  portion  of  the  cord  the  septum 
of  pia  mater  which  intervenes  between  these  two  strands  fails,  so  that 
it  is  only  in  the  upper  part  of  the  cord  that  they  are  marked  off  from 
each  other. 

In  the  lateral  and  anterior  columns  of  the  adult  cord  it  is  not  possible 
to  distinguish  the  different  strands  of  fibres  ;  and  yet  we  know  that  such 
exist,  possessing  different  functions  and  presenting  different  connexions. 
In  the  fcetal  cord,  however,  the  medullary  sheath  is  developed  at  a 
later  period  around  the  fibres  of  certain  tracts  than  in  the  case  of  others  ; 
and  if  thin  sections  of  developing  cords  be  subjected  to  the  Pal-Weigert 
staining  process,  the  tracts  in  which  the  medullary  sheaths  have  appeared 
are  dyed  black  and  stand  out  in  marked  contrast  to  the  non-medullated 
tracts  which  remain  pale  (Fig.  74).  In  the  present  instance  it  is  only 
necessary  to  indicate  the  three  best-defined  tracts  in  the  antero-lateral 
part  of  the  cord.  These  are  (1)  the  ascending  direct  cerebellar  tract; 
(2)  the  descending  crossed  pyramidal  tract ;  (3)  the  descending  direct 
pyramidal  tract. 

The  direct  cerebellar  tract  medullates  comparatively  early.  Conse- 
quently in  Fig.  74  it  stands  out  conspicuously  as  a  narrow  area  placed 
on  the  surface  of  the  cord,  in  the  posterior  part  of  the  lateral  column, 
immediately  in  front  of  the  postero-lateral  groove.  It  ascends  to  the 
cerebellum,  but,  traced  in  the  opposite  direction,  it  is  found  to  disappear 
in  the  lower  dorsal  area  of  the  cord.  The  crossed  pyramidal  tract,  when 
seen  in  transverse  section,  occupies  a  larger  district  of  the  cord.  Further, 
it  medullates  late,  and  the  area  which  it  occupies  appears  pale  in  Fig.  74. 
It  is  placed  in  the  lateral  column  in  front  of  the  posterior  horn  of  grey 
matter  and  immediately  internal  to  the  direct  cerebellar  tract.  As  the  direct 
cerebellar  tract  fails  in  the  lower  reaches  of  the  cord  the  crossed  pyramidal 
tract  comes  to  the  surface,  and  it  can  be  traced  as  low  as  the  fourth  sacral 
nerve.  The  direct  pyramidal  tract  forms  the  narrow  strip  of  the  anterior 
column  which  lies  immediately  adjacent  to  the  anteromedian  furrow. 
Like  the  crossed  pyramidal  tract  it  medullates  late,  and  therefore  in  Fig. 
74  it  appears  pale.  It  only  reaches  down  to  about  the  middle  of  the 
dorsal  region  of  the  cord  and  then  disappi 


VOL.   11—12 


178  HEAD   AND  NECK 


SIDE  OF  THE  NECK. 

Four  days  having  now  been  devoted  to  the  dissection  of 
the  posterior  aspect  of  the  body,  the  subject  is  turned  on  its 
back,  and  blocks  being  placed  under  the  thorax  and  pelvis, 
the  dissection  of  the  side  of  the  neck  is  commenced.  This 
region  may  be  said  to  present  a  somewhat  quadrilateral 
figure.  In  front,  it  is  bounded  by  the  middle  line  of  the 
neck ;  behind,  it  is  limited  by  a  line  corresponding  to  the 
anterior  margin  of  the  trapezius  muscle ;  below,  are  the  upper 
margin  of  the  manubrium  sterni  and  the  prominent  clavicle ; 
above,  the  base  of  the  lower  jaw,  the  mastoid  process,  and  the 
occiput. 

Surface  Anatomy. — Certain  important  landmarks  must 
be  recognised  before  the  skin  is  reflected  from  the  side  of 
the  neck.  The  sterno-mastoid  muscle,  pursuing  a  diagonal 
course  through  the  space  from  its  antero- inferior  to  its 
postero-superior  angle,  is,  perhaps,  the  most  essential  of 
these.  By  drawing  the  head  well  over  to  the  opposite  side, 
it  will  be  rendered  evident.  The  region  in  front  of  the 
sterno-mastoid  corresponds  to  the  anterior  triangle  of  the 
neck  ;  that  behind  it  constitutes  the  posterior  triangle.  Above 
the  notch  of  the  manubrium  sterni,  and  between  the  sternal 
tendons  of  the  two  sterno-mastoid  muscles,  the  deep  supra- 
sternal fossa  will  be  noted.  Subjacent  to  this  fossa  lies  the 
trachea,  but  it  is  only  in  emaciated  individuals  that  the  rings 
of  this  tube  can  be  felt  distinctly  from  the  surface.  In  its 
upper  part  the  trachea  is  obscured  by  the  isthmus  of  the 
thyroid  body  which  crosses  it. 

The  dissector  should  now  run  his  finger  upwards  in  the 
middle  line  of  the  neck.  Beyond  the  trachea  the  ring-like 
cricoid  cartilage  will  be  felt.  This  is  a  highly  important 
landmark.  With  it  as  his  guide  the  surgeon  is  able  to  mark 
out  the  points  at  which  the  trachea  or  larynx  may  be  opened, 
and  also  the  level  at  which  the  common  carotid  artery  is 
most  favourably  placed  for  the  application  of  a  ligature. 
Above  the  cricoid  cartilage  the  finger  enters  the  narrow 
interval  between  the  cricoid  and  thyroid  cartilages — a  gap 
which  is  occupied  by  the  tense  crico-thyroid  membrane.  In 
this  interval  the  operation  of  laryngotomy  may  be  performed. 


SIDE  OF  THE  NECK 


179 


Next  comes  the  thyroid  cartilage  with  its  prominent  po?mim 
Adami.  Beyond  the  thyroid  cartilage  is  an  interval  occupied 
by  the  thyro-hyoid  membrane,  and  bounded  above  by  the 
hyoid  bone.  The  body  and  cornua  of  the  hyoid  can  be 
plainly  felt  from  the  surface.  In  the  usual  attitude  of  the 
head  the  hyoid  bone  will  be  observed  to  be  placed  on  a 
level  with  the  lower  margin  of  the  mandible.  Above  the 
hyoid  bone,  between  it  and  the  symphysis  of  the  lower  jaw, 
is  the  anterior  part  of  the  floor  of  the  mouth. 

Dissection. — In  the  first  instance  merely  the  structures  superficial  to 
the  deep  cervical  fascia  should  be  dissected.  A  good-sized  block  being 
placed  under  the  shoulders  of  the  subject,  the  head  is  pulled  backwards 


Fig.   75. 


and  the  chin  dragged  over  to  the  opposite  side.     The  parts  will  be  put, 
still  further  on  the  stretch  if  the  shoulder  be  depressed  by  drawing  the  arm 
downwards  and  then  fixing  it  in  this  position. 

For  the  reflection  of  the  skin  three  incisions  are  required,  viz. — (1)  a 
vertical  incision  along  the  middle  line  of  the  neck,  from  the  chin  above  to 
the  sternum  below  ;  (2)  a  transverse  cut  from  the  lower  end  of  the  mesial 
incision  outwards  along  the  line  of  the  clavicle  to  the  acromion  process  of 
the  scapula  ;  (3)  an  oblique  incision,  beginning  above  at  the  mastoid  process 
behind  the  ear,  and  carried  downwards  and  forwards  along  the  anterior 
border  of  the  sterno-mastoid  muscle,  until  it  meets  the  middle  line  of  the 
neck  at  the  top  of  the  sternum. 

Two  triangular  flaps  of  skin,  corresponding  in  a  measure  to  the  two 
triangular  areas  of  the  neck,  are  thus  mapped  out,  and  must  now  be  carefully 
raised.  Throw  the  anterior  flap  upwards  towards  the  lower  jaw,  and  turn 
the  posterior  flap  backwards  towards  the  trapezius  muscle. 

Superficial  Fascia. — -The  superficial  fascia  in  this  region 
contains  in  its  midst  the  platysma  myoides  muscle — the  repre- 
sentative in  the  human  subject  of  the  panniculus  carnosus  in 
the  lower  animals.      In  the  male,   the  adipose  tissue  which 

[i—12a 


i So  HEAD  AND  NECK 

distinguishes  the  superficial  fascia  is  generally  very  sparse 
in  this  locality,  so  that  the  fleshy  fibres  of  the  muscle  are 
observed  shining  through  it.  In  females  and  children  the 
fat  is  more  abundant,  giving  a  fuller  and  more  rounded 
appearance  to  the  neck.  In  all  cases  the  fatty  tissue  is  most 
plentiful  between  the  chin  and  the  hyoid  bone,  forming  in 
stout  individuals  the  so-called  "double-chin." 

Dissection. — The  fibres  of  the  platysma  myoides  muscle,  which  run 
upwards  and  forwards,  must  now  be  cleaned  and  its  borders  defined.  In 
clearing  the  fatty  tissue  from  its  surface,  minute  nerve  filaments  will  be 
observed  piercing  it  to  reach  the  skin.  These  are  chiefly  branches  of  the 
superficial  cervical  nerve.  As  the  muscle  extends  downwards  on  to  the 
front  of  the  chest  and  upper  part  of  the  shoulder,  it  cannot  be  fully  studied 
until  the  dissector  of  the  arm  has  reflected  the  skin  from  these  regions. 

Platysma  Myoides. — This  is  an  exceedingly  thin  quadri- 
lateral sheet  of  muscular  fibres,  which  clothes  the  side  and 
front  of  the  neck,  and  lies  superficial  to  the  deep  fascia. 
Below,  it  takes  origin  by  scattered  and  sparse  fibres  from  the 
skin  and  subcutaneous  fascia  covering  the  upper  portions 
of  the  pectoralis  major  and  deltoid  muscles.  From  this 
it  proceeds  upwards  and  forwards  over  the  clavicle  and 
acromion,  but  obtains  little  or  no  attachment  to  these  bones. 
On  the  side  of  the  neck  it  decreases  somewhat  in  width,  and 
its  fibres  being  thus  more  closely  aggregated,  it  becomes 
thicker  and  more  distinct.  Finally,  it  reaches  the  lower  jaw, 
into  the  outer  surface  of  which  the  majority  of  the  fibres  are 
inserted,  many,  however,  blending  with  the  depressor  anguli 
oris.  The  anterior  fibres  decussate  below  the  chin  with 
the  corresponding  fibres  of  the  opposite  muscle,  whilst  the 
posterior  fibres  proceed  upwards  over  the  angle  of  the  jaw 
into  the  face,  and  curve  forwards  towards  the  angle  of  the 
mouth,  where  they  blend  with  the  facial  muscles  in  this 
locality. 

Reflection  of  the  Platysma. — This  must  be  done  very  carefully,  so  as 
not  to  injure  the  structures  which  lie  between  it  and  the  deep  fascia.  These 
are  (i)  the  external  and  anterior  jugular  veins;  (2)  the  descending  super- 
ficial branches  of  the  cervical  plexus,  which  are  especially  liable  to  injury 
as  they  cross  the  clavicle  and  acromion  process  ;  (3)  the  superficial  cervical 
nerve  and  cervical  division  of  the  facial  nerve  ;  and  (4)  the  superficial 
lymphatic  glands.  The  muscle  should  be  raised  from  below  upwards,  and 
left  attached  by  its  facial  connections. 

External  Jugular  Vein  (vena  jugularis  externa) — Fig.    76 
(10). — This  is  usually  a  vein  of  some  size.      It  will  be  seen 


SIDE  OF  THE  NECK  1S1 

emerging  from  the  substance  of  the  parotid  gland  immediately 
behind  the  angle  of  the  lower  jaw,  where  it  is  formed  by  the 
junction  of  the  posterior  auricular  vein,  and  posterior  division 
of  the  temporo-maxillary  vein.  From  this  it  descends  in  a 
nearly  vertical  direction  upon  the  deep  cervical  fascia,  taking 
a  course  which  may  be  mapped  out  on  the  surface  with 
tolerable  accuracy,  by  drawing  a  line  from  a  point  behind 
the  angle  of  the  jaw  to  the  middle  of  the  clavicle.  It  crosses 
the  sterno-mastoid  obliquely,  and,  reaching  the  posterior 
margin  of  this  muscle,  disappears  from  view  by  dipping 
through  the  deep  cervical  fascia  immediately  above  the 
clavicle.  It  will  subsequently  be  traced  to  its  termination 
in  the  subclavian  vein. 

Shortly  after  its  origin,  it  effects,  as  a  general  rule,  a 
communication  with  the  internal  jugular  vein,  and  lower 
down  one  or  more  superficial  twigs  may  connect  it  with  the 
anterior  jugular.  Half-way  down  the  neck  it  is  joined  by  a 
tributary  of  some  size,  which  comes  from  the  occipital  region 
and  the  back  of  the  upper  part  of  the  neck ;  this  vein  is 
termed  the  posterior  external  jugular. 

Superficial  Cervical  Glands. — These  form  a  group  of  small 
lymphatic  glands  which  lie  along  the  course  of  the  external 
jugular  vein.      They  vary  from  four  to  six  in  number. 

Anterior  Jugular  Vein  (vena  jugularis  anterior) — Fig.  76 
(23). — The  anterior  jugular  vein  is  small  in  comparison  with 
the  preceding.  It  begins  by  the  confluence  of  some  small 
veins  in  the  sub-maxillary  region,  and  descends  vertically  at 
a  short  distance  from  the  mesial  plane.  Immediately  above 
the  inner  end  of  the  clavicle  it  will  be  observed  to  dip  through 
the  deep  cervical  fascia.  It  terminates  by  turning  abruptly 
outwards  under  cover  of  both  heads  of  the  sterno-mastoid 
muscle,  and  opening  into  the  external  jugular  or  into  the 
subclavian  vein.  After  it  has  pierced  the  fascia,  a  short 
transverse  branch  which  crosses  the  mesial  plane  connects  it 
with  its  fellow  of  the  opposite  side. 

Superficial  Branches  of  the  Cervical  Plexus. — These  all 
take  origin  from  the  second,  third,  and  fourth  cervical  nerves, 
and,  emerging  from  under  cover  of  the  posterior  margin  of 
the  sterno-mastoid  about  its  middle,  pierce  the  deep  fascia, 
and  arrange  themselves  into  ascending,  transverse,  and  descending 
branches. 

The  ascending  branches  are  two  in  number,  and  both  have 
u—126 


182  HEAD  AND  NECK 

already  been  examined  in  the  superficial  dissection  of  the 
back  of  the  neck  (p.  135).  They  are  (a)  the  small  occipital 
— Fig.  76  (8),  —  springing  from  the  second  cervical  nerve,- 
and  (b)  the  great  auricular — Fig.  76  (5), — which  takes  origin 
from  the  second  and  third  cervical  nerves. 

The  transverse  branches  proceed  from  a  single  nerve  called 
the  superficial  cervical  nerve  (nervus  cutaneus  colli) — Fig.  76. 
This  arises  from  the  second  and  third  cervical  nerves,  and, 
winding  round  the  posterior  border  of  the  sterno-mastoid 
about  its  middle,  proceeds  transversely  forwards  upon  the 
deep  fascia  to  reach  the  area  over  the  anterior  triangle  of  the 
neck.  Here  it  divides  into  two  branches,  of  which  one  in- 
clines upwards  and  the  other  downwards.  The  upper  branch 
communicates  freely  with  the  cervical  division  of  the  facial 
nerve,  and  forms  one  or  more  wide  loops  with  it  in  the  region 
between  the  hyoid  bone  and  the  mandible  (Fig.  76).  Its 
branches  pierce  the  platysma  and  supply  the  skin  as  high  as 
the  base  of  the  lower  jaw.  The  lower  branch  can  be  traced  as 
low  as  the  sternum.  Its  branches  also  reach  the  skin  by 
piercing  the  platysma. 

The  descending  branches  take  origin  by  a  single  large  trunk 
from  the  third  and  fourth  cervical  nerves.  This  emerges 
from  under  the  posterior  border  of  the  sterno-mastoid,  and 
soon  breaks  up  into  several  twigs,  which  pierce  the  deep 
fascia  and  spread  out  widely  from  each  other  as  they  descend 
over  the  lower  part  of  the  posterior  triangle,  under  cover  of 
the  platysma.  The  ultimate  distribution  of  these  twigs  is  to 
the  integument  over  the  upper  part  of  the  front  of  the  chest 
and  over  the  shoulder.  To  gain  this  destination  they  are 
carried  downwards  over  the  clavicle  and  acromion  process, 
and  are  classified  into  three  groups  according  to  their  position 
— viz.,  (1)  acromial;  (2)  clavicular;  (3)  sternal — (Fig.  76). 

Cervical  Division  of  Facial  Nerve. — After  emerging  from 
the  parotid  gland  this  nerve  pierces  the  deep  fascia.  It  will 
be  found  immediately  below  the  angle  of  the  lower  jaw.  Its 
branches  spread  forwards  and  form  a  series  of  loops  which 
extend  as  low  down  as  the  hyoid  bone.  It  is  the  nerve  of 
supply  to  the  platysma  muscle,  and  effects  a  free  communica- 
tion with  the  upper  branch  of  the  superficial  cervical  nerve 
(Fig.  76). 

Deep  Cervical  Fascia  (fascia  colli)  —  Fig.  77. — The 
cervical   fascia  should  now  be  cleaned,   and    its   connexions 


.„  ■*    SIDE  OF  THE  NECK 


Fig.    76. — Superficial  Nerves  on  the  Side  of  the  Neck  and  Back  oi  the  Scalp. 
(Hirschfeld  and  Leveilte.) 


1.  Attollens  auriculam. 

2.  Posterior  belly  of  occipito- 

frontal is. 

3.  Retrahens  auriculam. 

4.  ( ireat  occipital  nerve. 

5.  (ireat  auricular  nerve. 

6.  Splenius  musj  lei 

7.  Sterno-ma  toid  muscle. 

B.    Sniall   occipital   nerve  (pre- 

s>ent  as  two  brancbe  1). 


9,  Great  auricular  nerve. 

10.  External  jugular  vein. 

11.  Superficial  cervical  nerve. 

12.  Spinal  accessory  nerve. 

1  j.   Desi  ending    branches   of 
cervical  plexus. 

14.  Cervical  branches  to   tra- 

pezius. 

1 5.  Trapezius  musclei 

j  16.  Clavicular  branches. 


17.  Acromial  branches. 

18.  Auricular   twigs  of  great 

auricular  nerve. 

19.  Parotid  gland. 

20.  Facial  nerve. 

21.  Masseter  mu 

22.  Infrft-matxlibular  nerve. 

23.  Anterior  jugular  vein. 

24.  Stomal  branches. 

25.  Platysma  myoides. 


184 


HEAD  AND  NECK 


studied.  It  constitutes  a  continuous  and  strong  aponeurotic 
envelope  for  the  neck,  very  much  in  the  same  manner  that 
the  brachial  aponeurosis  invests  the  upper  arm  or  the  fascia 
lata  the  thigh.  As  in  the  case  of  these  fasciae  also,  processes 
are  given  off  from  its  deep  surface  which  penetrate  into  the 
neck  to  form  sheaths  for  the  various  structures  enclosed 
within  the  general  investment.  Certain  of  these  processes 
stretch  across  the  mesial  plane  in  the  form  of  partitions  or 
septa,  which  subdivide  the  neck  into  fascial  compartments. 
Let  us  first  examine  the  general  envelope  as  it  is  at  present 


Depressor  muscles  of  the  larynx 
and  hyoid  bone\ 
Prevertebral  muscles 

Carotid  artery  and  its  sheath 
Sterno-mastoid 

Scalenus  amicus  . 
Platysma 


External 
jugular  vein 


Trachea 


Trapezius' 

Deep  muscles  on  back  of  neck'' 

FlG>  J7. — Diagrammatic  representation  of  a  transverse  section  through 
the  neck  at  the  level  of  the  isthmus  of  the  thyroid  body  to  show  the 
arrangement  of  the  cervical  fascia.      (Treves.) 

displayed,   and  then  we  shall  be  in  a  position  to  study  the 
more  important  septa  and  processes. 

The  envelope  formed  by  the  deep  cervical  fascia  is  not 
equally  developed  in  all  subjects.,  In  many  cases,  and  more 
especially  in  females,  it  is  thin  and  inconspicuous.  Neither 
is  it  of  equal  strength  at  all  points.  As  it  stretches  over  the 
triangles  of  the  neck,  it  is  distinctly  stronger  than  where  it 
covers  either  the  trapezius  or  sterno-mastoid.  Traced  back- 
wards, it  splits  at  the  anterior  border  of  the  trapezius  into  two 
lamellae  to  enclose  this  muscle.  The  superficial  layer  is  very 
thin,  and  both  blend  posteriorly  with  the  ligamentum  nuchae. 


SIDE  OF  THE  NECK  185 

When  the  investing  aponeurosis  is  followed  forwards  it  is 
found  to  split  again  at  the  posterior  border  of  the  sterno- 
mastoid  into  the  two  lamellae,  which  encase  that  muscle  and 
reunite  at  its  anterior  margin.  Of  these  layers  the  superficial 
is  so  delicate  that  the  fleshy  fasciculi  of  the  muscle  are  dis- 
tinctly seen  through  it.  From  the  sterno- mastoid  the 
aponeurosis  is  prolonged  over  the  anterior  triangle  to  the 
middle  line,  and  passes  continuously  over  to  the  opposite  side 
of  the  neck.  In  its  passage,  however,  from  one  side  toffee 
other,  it  obtains  a  firm  attachment  to  the  hyoid  bone.  |   r- — » 

Its  connexions  at  the  upper  and  lower  limits  of  the  neck  \J      / 
may  now  be  examined.     Above,  it  is  attached  along  the  whole  ^* 

length  of  the  base  of  the  lower  jaw.  Behind  the  angle  of  the 
jaw  it  is  carried  upwards  upon  the  surface  of  the  parotid 
gland,  as  the  parotid  fascia,  to  gain  attachment  to  the  lower 
margin  of  the  zygoma — a  connexion  which  will  be  afterwards 
seen  in  the  dissection  of  the  face.  Still  farther  backwards,  it 
is  fixed  to  the  mastoid  process,  and  to  the  superior  curved 
line  of  the  occipital  bone. 

Its  connexions  below  are  no  less  definite.  It  is  attached 
to  the  anterior  border  of  the  clavicle,  and  to  the  top  of  the 
sternum.  The  latter  attachment,  however,  is  of  a  somewhat 
intricate  character.  As  the  fascia  is  traced  downwards 
between  the  two  sterno-mastoid  muscles,  it  will  be  found  to 
split  a  short  distance  above  the  sternum  into  two  layers. 
Of  these,  the  superficial  layer  is  weak,  and  is  attached  to 
the  anterior  border  of  the  manubrium  sterni.  The  deeper 
layer  lies  immediately  in  front  of  the  sterno-hyoid  and  sterno- 
thyroid muscles,  and  is  fixed  below  to  the  posterior  border  of 
the  manubrium  sterni  and  to  the  inter-clavicular  ligament. 
Upon  either  side  the  two  layers  unite  beyond  the  sternal  head 
of  origin  of  the  sterno-mastoid ;  and  the  space  between  them 
contains — (1)  a  little  fatty  areolar  tissue ;  (2)  the  two  anterior 
jugular  veins  for  a  very  short  part  of  their  course ;  (3)  the 
cross  branch  of  communication  between  the  anterior  jugular 
veins  of  opposite  sides  when  this  exists ;  (4)  sometimes  a 
lymphatic  gland;  and  (5)  the  sternal  heads  of  the  sterno- 
mastoid  muscles.  Open  into  the  space  by  dividing  the 
anterior  layer  close  to  the  sternum,  and  gauge  its  extent  by 
means  of  the  handle  of  the  knife. 

The  processes  and  partitions  which  proceed  from  the  deep 
surface  of  the  cervical  fascia  cannot  in  every  case  be  displayed 


186  HEAD  AND  NECK 

at  the  present  stage  of  the  dissection,  but  it  is  necessary  that 
they  should  be  described,  in  order  that  the  student  may  be 
able  to  recognise  them  and  appreciate  their  bearings  as  they 
are  unfolded  in  the  subsequent  dissection  of  the  neck. 
Those  requiring  special  notice  are  : — 

1.  The  prevertebral  fascia. 

2.  The  pretracheal  fascia. 

3.  The  carotid  sheath. 

4.  The  stylo-maxillary  ligament. 

The  prevertebral  fascia  is  a  strong  partition  which  stretches 
across  the  neck  immediately  in  front  of  the  vertebral  column 
and  the  prevertebral  muscles.  On  either  side  it  extends  out- 
wards behind  the  carotid  vessels  and  the  internal  jugular  vein, 
to  obtain  attachment  to  the  layer  of  the  investing  aponeurosis 
which  lies  on  the  deep  surface  of  the  sterno-mastoid  muscle. 
In  an  upward  direction  it  can  be  traced  to  the  base  of  the 
skull  to  which  it  is  fixed,  whilst  below,  it  passes  continuously 
downwards  into  the  thorax  upon  the  longus  colli  muscles. 
The  prevertebral  fascial  septum  thus  subdivides  the  investing 
tube  of  cervical  fascia  into — (a)  a  posterior  compartment 
which  contains  the  vertebral  column  and  the  muscles  which 
surround  it ;  and  (p)  an  anterior  or  visceral  compartment,  which 
contains  the  pharynx,  the  larynx,  the  trachea,  the  gullet,  the 
thyroid  body,  and  the  depressor  muscles  of  the  larynx  and 
hyoid  bone.  It  is  important  to  note  that  there  is  no  barrier 
interposed  between  this  visceral  compartment  and  the  superior 
mediastinal  space  of  the  thoracic  cavity. 

The  pretracheal  fascia  is  a  partition  of  no  great  strength, 
which  springs  from  the  deep  aspect  of  the  lamella  clothing 
the  deep  surface  of  the  sterno-mastoid.  It  passes  right  across 
the  visceral  compartment  of  the  neck  in  front  of  the  thyroid 
body  and  trachea,  and  behind  the  anterior  belly  of  the  omo- 
hyoid, the  sterno-thyroid,  and  sterno-hyoid  muscles.  It  gives 
off  processes  which  ensheathe  the  thyroid  body  and  the 
trachea,  and  is  prolonged  downwards  into  the  thorax  in  front 
of  the  great  vessels  at  the  root  of  the  neck,  to  gain  an  attach- 
ment to  the  fibrous  layer  of  the  pericardium. 

The  great  vessels  of  the  neck  lie  under  cover  of  the  sterno- 
mastoid  muscle,  and  are  contained  within  the  outermost  part 
of  the  visceral  compartment  on  either  side  of  the  neck.  They 
are  enclosed  within  a  special  investment  of  fascia  which  re- 
ceives the  name  of  the  carotid  sheath.     Both  the  prevertebral 


SIDE  OF  THE  NECK  187 

and  the  pretracheal  septa  take  part  in  the  formation  of  this 
sheath,  and  in  addition  to  the  carotid  artery  and  the  internal 
jugular  vein  there  are  included  within  it  the  vagus  and  the 
descendens  hypoglossi  nerves.  Further,  the  gangliated  cord 
of  the  sympathetic  may  be  considered  to  be  embedded  in  its 
posterior  wall. 

The  stylo-maxillary  ligament  is  a  strong  process  of  the 
cervical  fascia  in  the  upper  part  of  the  neck,  which  passes 
from  the  angle  and  posterior  margin  of  the  lower  jaw  to  the 
styloid  process.  It  can  readily  be  exposed  at  the  present 
stage. 

Dissection. — The  sterno-mastoid  muscle,  as  we  have  observed,  divides 
the  side  of  the  neck  into  two  triangular  spaces — an  anterior  triangle  placed 
in  front  of  it,  and  a  posterior  triangle  behind  it.  This  muscle,  therefore, 
should  be  studied  before  proceeding  further.  Carefully  clean  its  superficial 
surface,  and  define  its  attachments.  It  may  also  be  raised  in  its  lower 
two-thirds  from  the  subjacent  layer  of  deep  cervical  fascia.  In  doing  this, 
care  must  be  taken  not  to  injure  the  sterno-mastoid  branch  of  the  superior 
thyroid  artery  which  will  be  seen  entering  its  deep  surface.  In  its  upper 
third  it  should  be  left  undisturbed  in  the  meantime. 

Sterno  -  Mastoid  (sternocleidomastoideus).  —  The  sterno- 
mastoid  muscle  takes  its  origin  below  by  two  heads  —  a 
sternal  and  a  clavicular.  The  sternal  head  is  rounded,  and 
chiefly  tendinous,  and  springs  from  the  upper  part  of  the 
anterior  face  of  the  manubrium  sterni.  The  clavicular  head  is 
broad  and  fleshy,  with  only  a  few  tendinous  fibres  intermixed, 
and  it  arises  from  the  inner  third  of  the  upper  surface  of  the 
shaft  of  the  clavicle.  A  narrow  interval  separates  these 
heads  below,  but  at  a  higher  level  the  sternal  portion  overlaps 
the  clavicular,  whilst  half-way  up  the  neck  they  both  unite 
into  a  fleshy  mass  which  ascends  to  the  mastoid  process  and 
occiput.  Here  the  muscle  expands  somewhat.  In  front,  it 
is  thick  and  tendinous,  and  is  inserted  into  the  fore-part  and 
outer  surface  of  the  mastoid  process  •  behind,  it  is  thin  and 
aponeurotic,  and  is  inserted  into  rather  more  than  the  outer 
half  of  the  superior  curved  line  of  the  occipital  bone.  In  the 
dissection  of  the  back,  this  latter  part  of  the  muscle  has  been 
detached  from  the  occiput. 

Dissection. — The  posterior  triangle  of  the  neck  should  be  dissected  first, 
for  this  purpose  the  shoulder  must  be  depressed  and  the  head  pulled  well 
over  to  the  opposite  side  and  supported  upon  a  block.  This  interferes,  of 
course,  with  the  dissection  of  the  axilla.  It  is  necessary,  therefore,  that 
the  dissectors  of  the  head  and  neck,  and  of  the  upper  limb,  should  arrange 
to  work  at  different  hours.      Again,  the  lower  part  of  the  posterior  triangle, 


1 88  HEAD  AND  NECK 

and  the  upper  part  of  the  axilla,  constitute  a  region  of  the  highest  import- 
ance to  both  dissectors,  seeing  that  it  is  here  the  great  blood  vessels  and 
nerves  leave  the  root  of  the  neck  and  enter  the  arm.  Arrangements, 
therefore,  must  be  made  for  each  to  have  an  opportunity  of  studying  these 
structures.  But  in  this  a  difficulty  arises.  Four  days  are  required  to 
complete  the  dissection  of  the  axilla,  whilst  two  days  are  amply  sufficient 
for  the  dissection  of  the  superficial  parts  of  the  neck  and  the  posterior 
triangle.  It  is  not  necessary,  however,  that  the  dissector  of  the  head  and 
neck  should  stop  work.  After  he  has  displayed  the  parts  in  the  space  as 
far  as  he  can  without  dividing  the  clavicle,  he  may  proceed  with  the  dis- 
section of  the  anterior  triangle,  and  on  the  fourth  day  return  to  the 
posterior  triangle  and  complete  the  work  with  the  co-operation  of  the 
dissector  of  the  arm. 

The  upper  part  of  the  posterior  triangle  has  already  been  displayed  in 
the  dissection  of  the  posterior  aspect  of  the  neck  (p.  137),  but  the  space 
can  only  be  studied  in  its  entirety  when  the  subject  is  placed  upon  its 
back.  The  trapezius  which  has  been  reflected  should  be  restored  as  far  as 
possible  to  its  natural  position  and  retained  by  means  of  a  stitch. 

When  the  investing  cervical  fascia  which  bridges  over  the  lower  part  of 
the  posterior  triangle  between  the  trapezius  and  the  sterno-mastoid  muscles 
is  removed,  a  variable  amount  of  fatty  areolar  tissue  is  exposed  in  the 
supraclavicular  region.  Embedded  within  this  will  be  found  the  trans- 
versalis  colli  and  the  suprascapular  vessels,  with  the  posterior  belly  of  the 
omo-hyoid  muscle  and  some  lymphatic  glands.  The  suprascapular  artery 
emerges  from  under  cover  of  the  sterno-mastoid,  and  passes  outwards 
immediately  subjacent  to  the  clavicle ;  the  transversalis  colli  artery  also 
comes  out  from  under  cover  of  the  sterno-mastoid,  but  it  lies  at  a  higher 
level.  The  posterior  belly  of  the  omo-hyoid  muscle  is  a  narrow  muscular 
band  which  appears  at  the  angle  which  is  formed  by  the  anterior  border  of 
the  trapezius  muscle  and  the  clavicle,  and  proceeds  forwards  and  upwards 
on  the  side  of  the  neck  to  disappear  under  cover  of  the  sterno-mastoid. 
It  should  be  noted  that  the  posterior  belly  of  the  omo-hyoid  muscle  is 
enveloped  in  a  sheath  of  fascia  which  is  loosely  disposed  around  it,  and  is 
then  prolonged  downwards  to  obtain  an  attachment  to  the  clavicle.  As 
the  muscle  disappears  under  cover  of  the  sterno-mastoid  it  gives  place  to  a 
rounded  tendon.  Upon  the  under  surface  of  this,  closely  applied  to  it, 
and  between  the  two  layers  of  fascia  which  invest  it,  will  be  found  a 
minute  nerve  twig  which  comes  from  the  ansa  hypoglossi,  and  ends  in 
this  portion  of  the  omo-hyoid.  The  lymphatic  glands  in  this  region  belong 
to  the  group  which  receive  the  name  of  inferior  deep  cervical  glands. 
When  the  fatty  areolar  tissue  is  removed  from  these  structures,  a  strong 
layer  of  fascia  spread  over  the  subclavian  vessels  and  the  brachial  nerves 
will  be  brought  into  view. 

Deep  Layer  of  Fascia  in  the  Supraclavicular  Region. — 

This  is  a  strong  sheet  of  fascia  which  is  spread  over  the 
brachial  nerves  and  the  subclavian  vessels.  When  traced 
inwards  under  cover  of  the  sterno-mastoid  it  will  be  observed 
to  cover  the  scalenus  anticus  muscle  and  to  become  con- 
tinuous with  the  prevertebral  fascia  and  the  posterior  part 
of  the  carotid  sheath.  In  a  downward  direction  it  may  be 
followed  into  the  axilla  as  the  sheath  of  the  axillary  vessels 
and   nerves,   and   here  it  establishes  a  connection  with   the 


SIDE  OF  THE  NECK  189 

costo-coracoid  membrane.  A  distinct  space  or  interval  exists 
between  this  deep  layer  of  fascia  and  the  investing  fascia  of 
the  neck.  This  interval  is  filled  with  fatty  areolar  tissue,  and 
also  contains  the  transversalis  colli  and  suprascapular  vessels, 
the  posterior  belly  of  the  omo-hyoid  muscle,  and  some  of  the 
inferior  deep  cervical  glands.  Seeing  that  the  investing 
cervical  fascia  is  attached  to  the  clavicle,  and  the  deep  layer 
of  fascia  is  more  or  less  intimately  connected  with  the 
costo-coracoid  membrane,  the  intra-aponeurotic  space  between 
them  extends  downwards  for  a  short  distance  behind  the 
clavicle.  An  incision  should  now  be  made  through  the  deep 
layer  of  fascia  as  it  lies  over  the  great  brachial  nerves.  If 
the  handle  of  the  knife  be  introduced  into  this  and  passed 
downwards  along  the  course  of  the  nerves  behind  the  fascia, 
it  will  be  found  to  proceed  with  the  greatest  freedom  into 
the  axilla. 

Dissection. — The  dissector  should  now  proceed  with  the  dissection  of 
the  posterior  triangle.  The  deep  layer  of  fascia  which  is  spread  over  the 
great  vessels  and  nerves  must  be  removed.  The  brachial  nerves  will 
then  be  seen  emerging  from  between  the  scalenus  anticus  and  the  scalenus 
medius  muscles.  At  this  stage  in  the  dissection  the  minute  nerve  of 
supply  to  the  subclavius  is  apt  to  be  injured.  It  passes  vertically  down- 
wards upon  the  superficial  aspect  of  the  brachial  nerves,  and  must  be 
secured  before  they  are  touched.  The  brachial  nerves  are  closely  matted 
together  by  dense  connective  tissue,  which  must  be  removed,  but  care 
must  be  taken  at  the  same  time  not  to  injure  the  branches  which  spring 
from  them.  When  the  lowest  trunk  of  the  brachial  plexus  is  reached  the 
subclavian  artery  will  come  into  view.  This  vessel  must  be  thoroughly 
displayed,  and  the  groove  on  the  first  rib  on  which  it  lies  may  be  rendered 
evident  by  scraping  the  bone  with  the  handle  of  the  knife.  By  tracing 
the  external  jugular  vein  downwards,  the  subclavian  vein  will  be  found 
lying  very  deeply  behind  the  clavicle.  The  scalenus  anticus  muscle,  with 
the  phrenic  nerve  passing  downwards  upon  its  anterior  surface,  will  also  be 
observed.     Both  lie  under  cover  of  the  sterno-mastoid  muscle. 

Posterior  Triangle. — This  is  a  long,  narrow,  triangular 
space  placed  between  the  posterior  border  of  the  sterno- 
mastoid  and  the  anterior  border  of  the  trapezius.  It  is 
covered  by  the  superficial  and  deep  fasciae  of  the  neck,  and 
also  in  its  lower  part  by  the  platysma  myoides  muscle. 
Certain  cutaneous  nerves  and  the  external  jugular  vein  have 
also  been  noticed  in  the  superficial  fascia  which  is  spread 
over  this  area.  Near  the  occiput  is  the  small  occipital  nerve ; 
near  the  clavicle  are  the  clavicular  descending  branches 
of  the  cervical  plexus,  and  a  very  short  portion  of  the 
external  jugular  vein. 


IQO 


HEAD  AND  NECK 


In  front,  the  posterior  triangle  is  bounded  by  the  posterior 
margin  of  the  sterno- mastoid,  and  behind,  by  the  anterior 
margin  of  the  trapezius.  The  base  which  is  below  is  formed 
by  the  middle  third  of  the  clavicle,  whilst  the  apex  which  is 


Occipital  artery 
t  ireat  occipital  nei 


Occipital  artery 

External  carotid  artery 
Facial  artery 

Hypoglossal  nerve 


Small  occipital  nerve 

Great  auricular  nerve 

Superficial  cervical  nerve 

Spinal  accessory  nerve 

Cervical  nerves  to  trapezius 

Scalenus  amicus 


Lingual  artery 
Superior  thyroid  artery 
Sterno-hyoid 


ransversalis  colli 

Brachial  nerves 
Suprascapular  artery 

Subclavian  artery 

Phrenic  nerve 
Subclavian  vein 

Interna]  mammary 


Internal  jugular  vein 
Sterno-hyoid 
Vagus 
Internal  jugular  vein 
Vertebral  vein 


Inferior  thyroid  artery 
Fig.  78. — Dissection  of  the  Posterior  Triangle  of  the  Neck. 

above  is  formed  by  the  meeting  of  the  sterno-mastoid  and 
trapezius  on  the  superior  curved  line  of  the  occipital  bone. 

The  posterior  belly  of  the  omo-hyoid,  which  crosses  the 
lower  part  of  the  posterior  triangular  space,  subdivides  it  into 
an  upper  portion  called  the  occipital  triangle,  and  a  lower 
part  termed  the  supraclavicular  or  subclavian  triangle. 

Occipital  Triangle. — The  occipital  or  upper  triangle  is 
much  the  larger  subdivision.     It  is  bounded  in  front  by  the 


SIDE  OF  THE  NECK  191 

sterno-mastoid ;   behind  by  the  trapezius  ;   whilst  its  base  is 
formed  by  the  omohyoid. 

Within  the  limits  of  the  occipital  triangle  we  find  the 
following  structures : — 

1.  The  occipital  artery  in  a  very  small  part  of  its  course,  and  only  when 

the  sterno-mastoid  fails  to  meet  the  trapezius  at  the  apex  of  the 
triangle. 

2.  The  spinal  accessory  nerve. 

3.  The  branches  from  the  third  and  fourth  cervical  nerves  which  cross 

the  space  to  supply  the  trapezius  muscle. 

4.  The  superficial  branches  of  the  cervical  plexus  as  they  appear  at  the 

posterior  border  of  the  sterno-mastoid  previous  to  piercing   the 
deep  fascia. 

5.  Branches  of  supply  to  the  levator  anguli  scapulae  from  the  third  and 

fourth  cervical  nerves. 

6.  The  transversalis  colli  artery  and  vein,  which  cross  the  lower  part  of 

the  space. 

7.  The  upper  part  of  the  brachial  plexus  of  nerves. 

The  contents  of  the  occipital  triangle  have  already  in  a 
great  measure  been  studied  (p.  137). 

Supraclavicular  Triangle. — The  supraclavicular  or  sub- 
clavian triangle  is  a  very  small  space.  It  is  bounded  above 
by  the  omo-hyoid ;  below  by  the  clavicle  ;  and  in  front  by 
the  sterno-mastoid.  The  area  thus  circumscribed  is  very 
variable  in  its  extent  in  different  subjects.  Indeed,  in  the 
natural  position  of  parts,  the  posterior  belly  of  the  omo-hyoid 
passes  forwards  so  close  to  the  clavicle  that  a  very  small 
interval  is  left  between  them,  and  it  is  only  after  the  fascial 
connexions  of  the  muscle  have  been  divided  that  the  triangle 
becomes  well  marked. 

Cases  also  occur  in  which  the  omo-hyoid  takes  partial  or  complete  origin 
from  the  clavicle,  and  thus  the  supraclavicular  space  is  still  further  reduced 
in  size.  Another  condition  which  materially  affects  the  dimensions  of  the 
supraclavicular  triangle  is  the  muscular  development  of  the  subject.  The 
more  powerful  the  neck,  the  more  extensive  are  the  attachments  of  the 
trapezius  and  sterno-mastoid  to  the  clavicle,  and  the  narrower  in  con- 
sequence is  the  triangle.  In  a  few  instances  these  muscles  will  be  observed 
to  meet  on  the  clavicle,  and  thus  obliterate  the  space  altogether.  This 
latter  condition,  however,  is  not  necessarily  associated  with  a  specially 
high  development  of  the  muscles. 

In  the  supraclavicular  space  a  great  number  of  highly 
important  structures  are  collected  together  within  a  very 
limited  area.  The  great  blood  vessels  and  nerves  which  pass 
from  the  neck  to  the  upper  limb  traverse  this  space.  Its 
contents  are  the  following  : — 


i92  HEAD  AND  NECK 

(  Subclavian. 
Arteries  -J    Transversalis  colli. 

(  Suprascapular. 

/   External  jugular. 
Veins      J    Suprascapular, 
veins      ^    Transversalis  colli. 

^  Subclavian. 
Nerves — The  trunks  of  the  brachial  plexus  and  their  branches. 
Lymphatic  glands. 

Subclavian  Artery  (arteria  subclavia).  —  It  is  only  the 
third  pari  of  the  subclavian  artery  which  is  included  in  the 
supraclavicular  triangle.  This  portion  of  the  vessel  extends 
from  the  outer  margin  of  the  scalenus  anticus  to  the  outer 
border  of  the  first  rib.  Here  it  enters  the  axilla  and  becomes 
the  axillary  artery.  It  takes  a  very  oblique  course ;  at  first  it 
lies  at  a  variable  distance  above  the  level  of  the  clavicle  ;  but 
as  it  runs  from  above  downwards  and  outwards,  it  finally 
comes  to  lie  behind  the  clavicle  and  the  subclavius  muscle. 

It  is  this  portion  of  the  artery  that  the  surgeon  selects,  when  the  choice 
lies  in  his  own  hands,  as  the  seat  for  applying  a  ligature.  Its  relations, 
therefore,  must  be  studied  with  especial  care. 

In  front  of  the  vessel  are  the  coverings  of  the  space  in 
which  it  lies — viz.,  superficial  fascia,  platysma,  superficial 
descending  clavicular  branches  of  the  cervical  plexus,  and 
the  deep  cervical  fascia.  Towards  its  termination,  how- 
ever, as  we  have  seen,  it  passes  behind  the  clavicle  and 
subclavius  muscle,  and  here  also  it  is  crossed  by  the  supra- 
scapular artery.  But  perhaps  the  most  important  anterior 
relation,  and  one  which,  in  tying  the  vessel,  may  somewhat 
embarrass  the  surgeon,  is  that  established  by  the  external 
jugular  vein  and  certain  of  its  tributaries.  This  vein  crosses 
in  front  of  the  artery  close  to  the  scalenus  anticus,  and  whilst 
occupying  this  position,  two,  or  it  may  be  three,  tributaries 
join  it — viz.,  the  transversalis  colli,  the  suprascapular,  and  the 
anterior  jugular  veins.  Observe  further  that  the  small  nerve 
to  the  subclavius  is  carried  vertically  downwards  in  front  of 
the  artery  behind  the  veins. 

Below,  the  third  part  of  the  subclavian  artery  rests  upon 
the  first  rib  ;  at  a  higher  level,  and  also  emerging  from  under 
cover  of  the  scalenus  anticus,  are  the  brachial  nerves.  Behind, 
the  vessel  is  in  contact  with  the  scalenus  medius,  although  the 
lowest  brachial  nerve  trunk  may  intervene  between  the  muscle 
and  the  artery.  The  subclavian  vein  is  placed  at  a  lower  level 
than  the  artery,  and  on  a  plane  slightly  anterior  to  it. 


SIDE  OF  THE  XECK  193 

Although,  as  a  rule,  no  branch  springs  from  this  portion 
of  the  subclavian,  it  is  not  uncommon  to  find  the  posterior 
scapular  artery  taking  direct  origin  from  its  upper  surface. 

Surgical  Anatomy. — The  dissector  should  again  examine  the  relations 
of  the  subclavian  artery,  with  the  view  of  determining  those  which  would 
constitute  the  most  trustworthy  guides  in  cases  where  it  is  necessary  to 
apply  a  ligature  to  its  third  part.  He  should  note  that  the  posterior  belly 
of  the  omo-hyoid  will  give  no  information  beyond  that  of  the  depth  at  which 
the  operator  has  arrived.  The  true  guide  is  the  outer  border  of  the  scalenus 
anticus  muscle.  This,  as  a  rule,  lies  immediately  subjacent  to  the  posterior 
margin  of  the  sterno-mastoid.  By  passing  the  forefinger  downwards  along 
the  outer  margin  of  the  scalenus  anticus,  the  scalene  tubercle  on  the  first  rib 
will  be  reached.  When  the  finger-nail  rests  on  this  tubercle  the  finger-pulp 
is  applied  to  the  artery,  and  in  the  living  subject  will  feel  its  pulsations. 

Suprascapular  and  Transversalis  Colli  Arteries. — Both  of 
these  arteries  will  be  observed  emerging  from  under  cover  of 
the  outer  border  of  the  sterno-mastoid.  Their  origin  from  the 
thyroid  axis  will  be  seen  in  a  subsequent  dissection. 

The  suprascapular  artery  (arteria  transversa  scapulae)  proceeds 
outwards  under  shelter  of  the  clavicle  and  across  the  third 
part  of  the  subclavian  artery  and  the  brachial  nerves.  At  the 
outer  limit  of  the  supraclavicular  triangle  it  passes  under 
cover  of  the  trapezius  to  reach  the  superior  border  of  the 
scapula  where  it  has  already  been  examined  (p.  139).  The 
transversalis  colli  (arteria  transversa  colli)  is  placed  at  a  higher 
level,  and  is  carried  outwards  across  the  posterior  triangle. 
It  passes  under  cover  of  the  posterior  belly  of  the  omo-hyoid, 
and,  as  a  rule,  superficial  to  the  brachial  nerves.  It  has 
already  been  observed  to  end  under  cover  of  the  anterior 
margin  of  the  trapezius,  by  dividing  into  the  posterior  scapular 
and  the  superficial  cervical  arteries  (p.  138). 

Veins. — The  arrangement  of  the  veins  has  been  noticed 
in  studying  the  relations  of  the  subclavian  artery.  The  ex- 
ternal jugular  vein,  as  a  rule,  crosses  the  third  part  of  this 
artery  at  the  outer  border  of  the  scalenus  anticus  and  joins 
the  subclavian  vein.  It  is  joined  close  to  its  termination  by 
the  suprascapular  and  transversalis  colli  veins,  and  perhaps 
by  the  anterior  jugular  as  it  emerges  from  under  cover  of 
the  sterno-mastoid.  In  certain  cases,  however,  the  anterior 
jugular  joins  the  subclavian  vein  directly. 

Floor  of  the  Posterior  Triangle. — The  floor  of  the  posterior 
triangular  space  is  formed  by  a  succession  of  muscles,  and  at 
its  very  lowest  part  by  a  small  portion  of  the  first  rib.  In 
the  occipital  subdivision  the  dissector  will  observe  that  the  floor 

vol.  11 — 13 


i94 


HEAD  AND  NECK 


is  constituted  "from  above  downwards  by — (i)  the  splenius 
capitis;  (2)  the  levator  anguli  scapulae;  and  (3)  by  the 
scalenus  medius  and  posticus.     At  the  apex  of  the  triangle  an 


c.v 


c.vi 


C.VII 


C.VIII 


D.ll 


Fig.  79.  — Diagram  of  the  Brachial  Plexus. 
S1,  S2,  S3. — The  three  subscapular  nerves.     Cir. — Circumflex  nerve. 

additional  factor  may  sometimes  be  observed — viz.,  a  small 
portion  of  the  complexus. 

In  the  supraclavicular  triangle  the  floor  lies  very  deeply. 
It  is  formed  by  the  scalenus  medius  and  posticus,  a  portion 
of  the  first  rib,  and  a  small  part  of  the  first  digitation  of  the 
serratus  magnus  muscle. 


SIDE  OF  THE  NECK  195 

Section  of  the  Clavicle.— In  order  that  a  satisfactory  view  may  be 
obtained  of  the  nerves  forming  the  brachial  plexus,  it  is  necessary  to  re- 
move the  middle  third  of  the  clavicle.  This,  of  course,  can  only  be  done 
when  the  dissector  of  the  upper  limb  has  completed  the  dissection  of  the 
axilla.  Saw  through  the  clavicle  at  two  points — viz.,  at  the  posterior 
margin  of  the  sterno-mastoid,  and  the  anterior  margin  of  the  trapezius — and 
remove  the  intermediate  piece  of  bone,  after  having  carefully  detached  it 
from  the  subclavius.  The  nerve  to  the  subclavius  should  now  be  traced 
to  its  distribution.  Then  divide  the  fibres  of  the  subclavius  which  still 
adhere  to  the  acromial  third  of  the  clavicle,  and  throw  the  muscle  inwards. 
This  will  allow  the  shoulder  to  drop  well  backwards. 

Brachial  Plexus. — This  great  nerve  plexus  is  formed  by 
the  anterior  primary  divisions  of  the  four  lower  cervical  nerves 
and  the  greater  part  of  the  large  anterior  primary  division  of 
the  first  dorsal  nerve.  Above,  the  plexus  is  further  rein- 
forced by  a  very  small  twig  of  communication  which 
passes  from  the  fourth  to  the  fifth  cervical  nerve ;  whilst 
belowT,  a  similar  connecting  twig  not  infrequently  passes 
upwards  in  front  of  the  neck  of  the  second  rib  from  the 
second  to  the  first  dorsal  nerve.  The  four  lower  cervical 
nerves  are  brought  into  connection  with  the  middle  and 
inferior  ganglia  of  the  cervical  sympathetic  by  means  of  fine 
grey  rami  communicantes. 

The  great  brachial  nerves  emerge  from  the  interval  between 
the  scalenus  anticus  and  scalenus  medius,  and  proceed  down- 
wards and  outwards  through  the  lower  part  of  the  posterior 
triangle  towards  the  axilla.  The  manner  in  which  they  unite 
to  form  the  plexus  is  upon  the  whole  very  constant.  The 
fifth  and  sixth  nerves  unite  to  form  an  upper  trunk  ;  the  seventh 
nerve  remains  single  and  proceeds  downwards  as  a  middle 
trunk ;  and  the  eighth  cervical  and  first  dorsal  nerves  join, 
whilst  still  under  cover  of  the  scalenus  anticus,  to  constitute 
a  third  or  lower  trunk.  Whilst  still  within  the  posterior 
triangle  of  the  neck,  each  trunk  splits  into  an  anterior  and  a 
posterior  division.  Raise  the  three  anterior  divisions  on  the 
handle  of  the  knife,  and  then  it  will  be  seen  that  the  three 
posterior  divisions  unite  to  form  the  posterior  cord  of  the  plexus, 
and,  further,  that  the  innermost  of  these  divisions  is  much 
smaller  than  the  other  two.  Of  the  three  anterior  divisions, 
the  outer  two  join  to  constitute  the  outer  cord,  whilst  the  inner- 
most is  carried  down  by  itself  as  the  inner  cord  of  the  plexus. 
From  the  three  cords  of  the  brachial  plexus  are  given  off  the 
branches  which  supply  the  upper  limb. 

From  the  above  description  it  will  be  seen  that  the  plexus, 
ir— 13a 


196 


HEAD  AND  NECK 


from  changes  which  are  effected   in  the  arrangement  of  its 
fibres,  may  be  divided  into  four  stages : — 


1st  Stage. 

2nd  Stage. 

3rd  Stage. 

4th  Stage. 

5  separate 
nerves  (viz., 

4  lower 
cervical  and 
first  dorsal). 

3  nerve 
trunks  (viz., 

an  upper, 

middle,  and 

lower). 

3  anterior 

divisions  and 

3  posterior 

divisions. 

3  nerve 

cords  (viz., 

an  outer, 

inner,  and 

a  posterior). 

The  first  three  of  these  stages  are  generally  observed  in  the 
lower  part  of  the  posterior  triangle  and  in  the  upper  part  of 
the  axilla.  It  must  be  understood,  however,  that  the  points 
at  which  division  and  union  of  the  different  parts  of  the 
plexus  takes  place  are  subject  to  considerable  variation. 

Supraclavicular  Branches  of  the  Brachial  Plexus. — The 
only  branches  of  the  brachial  plexus  which  fall  to  the  lot  of 
the  dissector  of  the  head  and  neck  are  those  given  off  above 
the  level  of  the  clavicle.  These  are  for  the  most  part  destined 
for  the  supply  of  muscles  in  the  neighbourhood.     They  are  : — 

1.  Nerve  to  rhomboids,     from  the  5th  cervical  nerve. 

2.  Nerve  to  subclavius,  1  r        t,      „.,        ■,  <■.*  •     , 

„    c  ,  '    -  irom  the  Sth  and  6th  cervical  nerves. 

3.  Suprascapular,  J  J 

^"  r  d  1 1  r  from  the  5th,  6th,  and  7th  cervical  nerves, 

nerve  of  Bell,  J  J    '        '  * 

5.   Twigs      to      scalene  I  r  , ,      ,  r  .     ,  , 

J  °  .  1  ,  irom   the  lower  four  cervical  nerves  close  to 

muscles  and  longus  Y      .,     .   ,  .  ,      ,  r 

,,•  fa  the  intervertebral  foramina. 


Communicating:  twig;  \  c  .,  .     , 

.       ,        •        °        fe  }  from  5th  cervical, 
to  phrenic  nerve,      J  J 


The  nerve  to  the  rhomboids  (nervus  dorsalis  scapulae)  is  a 
long  slender  branch  which  springs,  by  a  stem  common  to  it 
and  the  uppermost  root  of  the  nerve  of  Bell,  from  the  back 
of  the  fifth  cervical  nerve  as  it  lies  upon  the  scalenus  medius. 
Draw  the  fifth  cervical  nerve  forwards,  and  the  branch  in 
question  will  be  seen  passing  backwards  through  the  fibres  of 
that  muscle  to  reach  the  deep  surface  of  the  levator  anguli 
scapulae.  It  here  meets  the  posterior  scapular  artery,  and 
proceeds  with  it  downwards  under  cover  of  the  rhomboid 
muscles  close  to  the  base  of  the  scapula.  It  supplies  one  or 
two  twigs  to  the  levator  anguli  scapulae,  and  is  finally  exhausted 
in  the  rhomboids. 


SIDE  OF  THE  NECK  i97 

The  nerve  to  the  subdavius  (nervus  subclavius)  is  a  minute 
twig  which  springs  from  the  front  of  the  upper  trunk  of  the 
plexus,  and  then  passes  vertically  downwards  upon  the  plexus, 
and  across  the  subclavian  artery  to  the  subclavius  muscle, 
which  it  reaches  by  piercing  the  posterior  lamina  of  its  sheath. 

A  communication  between  the  nerve  to  the  subclavius  and  the  phrenic 
is  by  no  means  uncommon.  This  connecting  filament  may  join  the  phrenic 
in  the  neck  or  in  the  thorax.  In  all  probability,  it  represents  that  com- 
municating twig  (or  at  least  a  portion  of  it)  which,  on  other  occasions, 
passes  directly  from  the  fifth  cervical  nerve  to  the  phrenic. 

The  suprascapular  nerve  (nervus  suprascapularis)  is  the 
largest  branch  given  off  above  the  clavicle.  It  springs  from 
the  back  of  the  upper  trunk  of  the  plexus,  and  runs  down- 
wards, outwards,,  and  backwards,  at  a  higher  level  than  the 
brachial  nerves,  to  the  suprascapular  notch  of  the  scapula, 
through  which  it  enters  the  supraspinous  fossa.  As  it 
approaches  the  scapula,  it  passes  under  cover  of  the  trapezius 
and  posterior  belly  of  the  omo-hyoid,  and  comes  into  relation 
with  the  artery  of  the  same  name. 

The  external  respiratory  nerve  of  Bell,  also  called  the  posterior 
thoracic  (nervus  thoracicalis  longus),  is  formed  by  the  union 
of  three  roots  which  arise  from  the  back  of  the  fifth,  sixth, 
and  seventh  cervical  nerves  close  to  the  intervertebral  foramina. 
The  roots  from  the  fifth  and  sixth  cervical  nerves  pass  back- 
wards through  the  fibres  of  the  scalenus  medius,  and  unite 
into  one  stem  which  gives  branches  to  the  upper  part  of  the 
serratus  magnus.  The  third  root  from  the  seventh  cervical 
nerve  does  not  pierce  the  scalenus  medius.  It  is  carried 
downwards  on  the  surface  of  that  muscle,  and  ultimately  joins 
the  stem  formed  by  the  union  of  the  upper  two  roots.  The 
posterior  thoracic  nerve  enters  the  axilla  behind  the  axillary 
vessels,  and  is  entirely  devoted  to  the  supply  of  the  serratus 
magnus  muscle. 

Dissection.— At  this  stage,  the  dissector  of  the  upper  limb  removes  the 
arm  from  the  trunk.  The  dissector  of  the  head  and  neck  must  see  that 
the  vessels  and  nerves  are  not  cut  too  short.  The  outer  border  of  the  first 
rib  is  the  level  at  which  they  should  be  divided. 

The  dissector  should  now  proceed  with  the  dissection  of  the  anterior 
triangle.  In  this  dissection  the  visceral  compartment  of  the  neck  is  opened 
up,  and  its  contents  displayed.  Let  the  head  hang  well  over  the  end  of 
the  table,  and,  raising  the  lower  jaw  as  much  as  possible,  fix  it  in  this 
position  by  means  of  hooks.  Ik-gin  the  dissection  by  throwing  the  super- 
ficial cervical  nerve  and  the  cervical  division  of  the  facial  nerve  backwards, 
and  then  carefully  raise  the  cervical  fascia  from  the  area  in  front  of  the 
H—13  6 


198  HEAD  AND  NECK 

sterno-mastoid.  The  anterior  triangle  is  subdivided  into  4jir.ee  smaller 
triangles  by  three  muscles  which  traverse  it  in  different  directions.  These 
muscles  are  : — (i)  the  anterior  belly  of  the  omo-hyoid  ;  (2)  the  digastric  ; 
and  (3)  the  stylo-hyoid.  It  is  well,  therefore,  at  this  stage  to  define  these 
muscles,  and  accurately  determine  the  precise  position  and  extent  of  each 
subdivision  of  the  space.  The  anterior  belly  of  the  omo-hyoid  appears  by 
emerging  from  under  cover  of  the  anterior  border  of  the  sterno-mastoid,  a 
short  distance  above  the  sternal  origin  of  the  latter.  It  crosses  the  space  very 
obliquely,  running  upwards  and  forwards  to  the  body  of  the  hyoid  bone. 
The  digastric,  as  its  name  implies,  is  a  two-bellied  muscle.  The  posterior 
belly  comes  out  from  under  cover  of  the  sterno-mastoid,  close  to  the  mastoid 
process,  and  behind  the  lower  part  of  the  parotid  gland.  It  proceeds 
downwards  and  forwards  to  the  hyoid  bone,  and  there  the  intermediate 
tendon  is  developed.  The  anterior  belly  is  directed  upwards  and  forwards 
to  the  symphysis  of  the  lower  jaw.  The  intermediate  tendon  of  the 
digastric  muscle  is  bound  down  to  the  hyoid  bone  by  a  process  of  deep 
fascia  ;  and  in  cleaning  the  muscle,  care  must  be  taken  not  to  detach  this. 
The  stylo-hyoid  muscle  lies  on  a  deeper  plane  than  the  posterior  belly  of  the 
digastric,  and  in  relation  to  its  upper  border.  It  is  pierced  by  the  digastric 
tendon  at  the  hyoid  bone.  In  the  first  instance,  merely  clean  the  superficial 
surface  of  these  muscles.  In  the  case  of  the  anterior  belly  of  the  omo-hyoid, 
care  must  be  taken  not  to  injure  the  twigs  from  the  descendens  hypoglossi 
nerve,  which  enter  its  upper  or  outer  border,  and,  whilst  dealing  with  the 
digastric  muscle,  bear  in  mind  that  the  facial  vein,  and  the  anterior  division 
of  the  temporo-maxillary  vein,  usually  descend  superficial  to  its  posterior 
belly,  and  must  be  secured  before  the  muscle  is  touched.  The  filaments 
from  the  mylo-hyoid  nerve,  which  enter  the  upper  border  of  its  anterior 
belly,  are  not  liable  to  injury  if  ordinary  caution  be  exercised. 

Anterior  Triangle  of  the  Neck. — The  anterior  triangle 
differs  from  the  posterior  triangle  in  having  its  base  above  and 
its  apex  below.  It  is  bounded  behind  by  the  anterior  margin 
of  the  sterno-mastoid,  and  in  front  by  the  middle  line  of  the 
neck.  Its  base  is  formed  by  the  inferior  margin  of  the  lower 
jaw,  and  a  line  drawn  from  the  angle  of  the  mandible  to  the 
sterno-mastoid  muscle,  whilst  its  dependent  apex  is  constituted 
by  the  meeting  of  its  anterior  and  posterior  limits  at  the 
upper  border  of  the  sternum. 

Spread  over  the  anterior  triangle  there  are  the  skin,  the 
superficial  fascia  with  the  platysma,  and  the  deep  cervical 
fascia.  In  the  interval  between  the  platysma  and  the  deep 
fascia  are  placed  the  branches  of  the  superficial  cervical  nerve, 
the  cervical  branch  of  the  facial  nerve,  and  also  the  anterior 
jugular  vein. 

Subdivisions  of  the  Anterior  Triangle. — Distinctive  terms 
are  applied  to  the  three  subsidiary  triangles  which  are  mapped 
out  within  the  area  of  the  anterior  triangular  space  by  the 
anterior  belly  of  the  omo-hyoid  muscle  and  the  two  bellies  of 
the  digastric  muscle.      The  lowest  subdivision  is  termed  the 


SIDE  OF  THE  NECK 


199 


lower  or  muscular  triangle;  the  intermediate  space  receives 
the  name  of  carotid  triangle ;  whilst  the  highest  subdivision  is 
called  the  submaxillary  or  digastric  triangle  (Fig.  80). 

The  muscular  triangle  is  bounded  in  front  by  the  middle 
line  of  the  neck,  and  behind  by  the  sterno-mastoid.  Its  base  is 
above,  and  is  formed  by  the  anterior  belly  of  the  omo-hyoid, 
whilst  its  apex  is  below  at  the  upper  margin  of  the  sternum. 

The  carotid  triangle  is  limited  above  by  the  posterior  belly 


Occipital  triangle 


Subclavian  triangle 


Digastric  triangle 
Carotid  triangle 

Muscular  triangle 


Fig.  80. — Diagram  to  show  the  Boundaries  of  the  Triangles  of  the  Neck. 


of  the  digastric,  and  below  by  the  anterior  belly  of  the  omo- 
hyoid. Its  base  is  directed  backwards,  and  is  formed  by  the 
sterno-mastoid,  whilst  its   apex  is  at  the  hyoid  bone. 

The  digastric  triangle  is  bounded  below  and  behind  by  the 
posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscle, 
and  below  and  in  front  by  the  anterior  belly  of  the  digastric. 
Its  base  is  above,  and  is  constituted  by  the  body  of  the  lower 
jaw,  and  a  line  drawn  backwards  from  the  angle  of  the 
mandible  to  the  sterno-mastoid  muscle ;  its  apex  points  down- 
wards, and  is  formed  by  the  intermediate  tendon  of  the 
digastric  muscle. 


200  HEAD  AND  NECK 

Dissection. — The  numerous  and  diverse  structures  contained  within  the 
anterior  triangle  must  now  be  displayed.  This  is  a  dissection  which 
requires  some  preliminary  knowledge  of  the  parts  to  be  exposed.  The 
student  is  therefore  advised  to  read  the  general  account  which  is  given  of 
the  parts  which  are  brought  into  view,  as  each  subdivision  of  the  space  is 
opened  up  (p.  200  to  p.  204),  before  undertaking  the  work.  The  dissec- 
tion should  be  carried  out  over  the  entire  area  at  once,  and  the  structures 
found  in  one  subdivision  followed  upwards  or  downwards,  as  the  case  may 
be,  into  the  other  subdivisions  of  the  space.  It  is  a  common  fault  with 
dissectors  to  fail  to  open  up  the  digastric  triangle  until  the  two  lower 
triangles  have  been  fully  dissected.  Two  small  nerves  are  especially  liable 
to  injury,  and  therefore  should  be  secured  as  early  as  possible.  They  are 
the  thyro-hyoid  branch  of  the  hypoglossal  nerve  and  the  external  laryngeal 
nerve.  The  hypoglossal  nerve,  which  will  be  found  crossing  the  carotid 
triangle  at  the  lower  border  of  the  posterior  belly  of  the  digastric,  should 
be  traced  forwards  ;  as  it  approaches  the  hyoid  bone,  its  minute  thyro- 
hyoid branch  will  be  discovered,  leaving  its  lower  border  at  an  acute  angle, 
and  proceeding  downwards  and  forwards  to  reach  the  thyro-hyoid  muscle. 
The  external  laryngeal  nerve  is  a  long  slender  branch  which  occupies  a 
deeper  plane.  To  expose  it  the  carotid  vessels  should  be  pulled  outwards 
from  the  larynx,  and  the  loose  tissue  in  the  interval  thus  opened  up  divided 
carefully  in  an  oblique  direction  and  along  a  line  connecting  the  cricoid 
cartilage  with  the  bifurcation  of  the  common  carotid  artery.  The  nerve 
will  be  found  as  it  passes  downwards  and  forwards  to  disappear  under  cover 
of  the  depressor  muscles  of  the  larynx.  It  will  be  traced  to  its  ultimate 
distribution  at  a  subsequent  stage  of  the  dissection. 

Muscular  Triangle. — As  this  triangle  is  gradually  opened 
up,  the  following  structures  will  come  into  view : — 

1.  The  sterno-hyoid  and  sterno-thyroid  muscles. 

2.  The  branches  from  the  ansa  hypoglossi  to  these  muscles. 

3.  The  external  laryngeal  nerve. 

4.  The  superior  thyroid  artery. 

5.  The  greater  part  of  the  larynx,  the  thyroid  body,  and  the  trachea. 

6.  The  oesophagus  on  the  left  side. 

7.  The  recurrent  laryngeal  nerve. 

When  the  fascia  is  removed  from  this  part  of  the  anterior 
triangle,  the  only  structures  which  are  seen  within  its  limits 
are  the  sterno-hyoid  and  sterno-thyroid  muscles.  It  is  for 
this  reason  that  the  term  muscular  is  applied  to  the  space. 
As  the  dissection  is  proceeded  with,  however,  the  large  nerve 
of  supply  for  these  muscles,  which  comes  from  the  ansa  hypo- 
glossi, will  be  found  lying  near  the  outer  border  of  the  sterno- 
thyroid and  breaking  up  into  numerous  twrigs.  Towards  the 
upper  part  of  the  space  the  superior  thyroid  artery  will  be 
noticed  passing  downwards  under  cover  of  the  omo-hyoid, 
sterno-thyroid,  and  sterno-hyoid  muscles  to  reach  the  thyroid 
body.  At  a  slightly  higher  level  than  this  artery,  the  external 
laryngeal    nerve   runs   forwards   to   end    in   the   crico-thyroid 


SIDE  OF  THE  NECK 


20I 


muscle.  Under  cover  of  the  sterno-hyoid  and  sterno-thyroid 
muscles  will  be  observed  the  larynx,  the  isthmus  and  a  con- 
siderable part  of  the  lateral  lobe  of  the  thyroid  body,  and  the 
trachea.  The  recurrent  laryngeal  nerve  lies  deeply.  It  will 
be  found  in  the  interval  between  the  gullet  and  trachea.  As 
the  oesophagus  inclines  to  the  left  behind  the  trachea,  it  follows 
that  it  is  only  seen,  when  in  its  natural  position,  in  the  left 
muscular  triangle. 

Carotid   Triangle. — During  the  dissection  of  the  carotid 
triangle  the  following  parts  are  displayed : — 

,   Common  carotid  dividing  into  external  and  internal 
carotid  arteries. 


Arteries 


Veins 


2.  Superior  thyroid. 

3.  Lingual. 

4.  Facial. 

5.  Occipital. 

^6.  Ascending  pharyngeal. 

fi.   Internal  jugular. 

2.   Facial. 
I  3.   Anterior  temporo-maxillan 
,    Lingual. 
Superior  thyroid. 
Middle  thyroid. 


Branches  of 
the  external 
carotid. 


Tributaries  of  the 
internal  jugular. 


Nerves 


Hypoglossal. 


f  Crossing  the  space  in  a 

^  transverse  direction. 


2.  Descendens  hypoglossi. 

3.  Nerve  to  thyro-hyoid.  Crossing 

4.  Internal  laryngeal.  !••       the  space 

5.  External  laryngeal.  obliquely. 

6.  Spinal  accessory.  J 

7.  Vagus.  )  Descending 
^8.  Sympathetic.     J          vertically. 

Carotid  body. 

Portion  of  the  larynx  and  pharynx. 
( Greater  cornu  of  the  hyoid  bone. 
Lymphatic  vessels  and  glands. 

This  subdivision  of  the  anterior  triangle,  when  opened 
up,  contains  portions  of  each  of  the  three  carotid  arteries. 
It  therefore  receives  the  name  of  carotid  triangle.  It  is 
well,  however,  that  the  dissector  should  clearly  understand 
that  it  is  only  after  the  parts  are  relaxed  by  dissection  that 
these  vessels  come  to  lie  within  the  space.  When  the 
fascia  and  platysma  are  in  position  they  are  completely 
overlapped  by  the  sterno-mastoid  muscle.  The  common 
carotid  artery  is  enveloped,  along  with  the  internal  jugular 
vein  and  vagus  nerve,  in  a  common  sheath  of  fascia.     The 


202  HEAD  AND  NECK 

carotid  sheath  should  be  slit  open,  care  being  taken  of  the 
descendens  hypoglossi  nerve,  which  also  descends  obliquely 
within  it.  The  intimate  connexion  which  this  sheath  pre- 
sents with  the  prevertebral  layer  of  fascia  can  now  be  made 
out.  The  common  carotid  usually  bifurcates  opposite  the 
upper  border  of  the  thyroid  cartilage.  Observe  that  the 
internal  carotid  artery  at  first  lies  behind,  and  to  the  outer  side 
of  the  external  carotid.  Upon  the  coats  of  these  vessels 
numerous  sympathetic  twigs  ramify,  and,  at  the  point  of 
bifurcation  of  the  common  carotid,  a  small  oval  body,  termed 
the  carotid  body,  will  be  found  closely  applied  to  the  deep 
surface  of  the  vessel.  The  branches  of  the  external  carotid 
which  take  origin  in  the  area  of  this  triangle  run  for  only 
a  very  short  part  of  their  course  within  it.  Three  branches 
will  be  noticed  springing  from  the  anterior  aspect  of  the 
external  carotid.  Named  from  below  upwards  these  are:  (i) 
the  superior  thyroid  artery,  which,  after  having  given  off  its 
hyoid,  superior  laryngeal,  and  sterno-mastoid  branches,  disappears 
under  cover  of  the  omo-hyoid  muscle,  and  enters  the  mus- 
cular triangle;  (2)  the  lingual  artery,  which  forms  a  small 
loop  or  arch  above  the  great  cornu  of  the  hyoid  bone  and 
leaves  the  space  by  passing  under  cover  of  the  digastric  and 
stylo-hyoid  muscles  ;  and  (3)  the  facial  artery,  which  ascends 
under  the  same  muscles  to  gain  the  digastric  triangle.  The 
occipital  artery  commonly  springs  from  the  posterior  aspect  of 
the  external  carotid  close  to  the  lower  border  of  the  digastric, 
and  soon  quits  the  space  by  running  upwards  and  backwards 
under  cover  of  the  sterno-mastoid  muscle.  The  sterno-mastoid 
branch  of  the  occipital  artery  comes  off  as  the  latter  leaves 
the  triangle,  and  accompanies  the  spinal  accessory  nerve. 
The  ascending  pharyngeal  artery  will  be  found  by  separating 
the  external  and  internal  carotid  arteries  from  each  other, 
and  dissecting  between  them.  It  springs  from  the  posterior 
aspect  of  the  former  about  half  an  inch  above  its  origin, 
and  then  takes  a  vertical  course  upwards  on  the  prevertebral 
muscles. 

The  internal  jugular  vein,  which  from  a  surgical  point  of 
view  is  the  most  important  structure  in  the  anterior  triangle 
of  the  neck,  lies  close  to  the  outer  side  of  the  common 
carotid  artery,  and  is  included  within  the  same  fascial  sheath. 
Several  tributaries  join  it  as  it  passes  through  the  carotid 
triangle.     The  most  conspicuous  of  these  is  the  common  facial 


SIDE  OF  THE  NECK  203 

vein,   which   is   formed  by  the  union  of  the  facial  vein  and 
the    anterior  division   of  the    temporo- maxillary  vein.     The 
common  facial  vein  enters  the  internal  jugular  at  the  level 
of  the  hyoid  bone,  and  certain  lymphatic  glands  which  over- 
lie the  veins  at  this  point  are  of  especial  importance,  seeing 
that  they  are  frequently  the  seat  of  tubercular  disease  (Stiles). 
The  nerves  which  are  brought  into  view  as   the  carotid 
triangle  is  gradually  opened  up  are  very  numerous,  but  they 
can  be  classified  according  to  the  direction  which  they  take 
through  the  space.      One  large  nerve,  the  hypoglossal,  takes 
a  more  or  less  transverse  course  across  the  upper  part  of  the 
space.      It  forms   a  loop   across  this  part   of  the   neck  im- 
mediately below   the  lower  margin  of  the  digastric   muscle. 
Two   descend  vertically — viz.,   the  vagus  and   the  gangliated 
cord  of  the   sympathetic.     The   vagus  lies   in  the  posterior 
part   of   the   carotid    sheath    between    the    common    carotid 
artery  and   the  internal  jugular  vein.      The  syt7ipathetic  cord 
is    embedded   in   the   posterior    wall   of  the  carotid  sheath. 
The   remaining   five   nerves   traverse    the  triangle   obliquely. 
Four    run    from    above   downwards    and   forwards,    viz.,    the 
descendens    hypoglossi,   the    thyro- hyoid,    the    internal    and 
external  laryngeal  nerves ;  and  one — the  spinal  accessory — 
is  directed  from  above  downwards  and  backwards. 

The  descendens  hypoglossi  springs  from  the  hypoglossal 
nerve  as  it  hooks  round  the  occipital  artery,  and  descends 
within  the  carotid  sheath.  It  is  joined  at  the  upper  border 
of  the  omo-hyoid  by  one  or  two  branches  from  the  cervical 
plexus,  and  in  this  manner  the  ansa  hypoglossi  is  formed. 
The  thyro-hyoid  is  a  minute  nerve  which  arises  from  the 
hypoglossal  nerve  before  it  disappears  under  cover  of  the 
posterior  belly  of  the  digastric.  The  internal  laryngeal  nerve 
descends  behind  the  carotid  vessels.  It  will  be  readily 
found,  with  the  corresponding  artery,  in  the  interval  between 
the  hyoid  bone  and  upper  border  of  the  thyroid  cartilage. 
It  enters  the  larynx  by  piercing  the  thyro-hyoid  membrane. 
The  external  laryngeal  nerve  is  a  much  smaller  twig.  It  leaves 
the  space  by  passing  under  cover  of  the  depressor  muscles  of 
the  larynx  and  hyoid  bone.  The  spinal  accessory  ?ierve  is 
placed  high  up  in  the  interval  between  the  digastric  and  the 
sterno-mastoid  muscles.  It  soon  disappears  by  sinking  into 
the  substance  of  the  sterno-mastoid  about  one  and  a  half 
inches  below  the  lip  of  the  mastoid  process. 


2o4  HEAD   AND   NECK 

Digastric  Triangle. — The  digastric  space  may  be  divided 
very  conveniently  into  an  anterior  and  posterior  part  by  the 
stylo-maxillary  ligament  and  a  line  drawn  downwards  from 
it.  The  portion  in  front  has  a  distinct  floor,  composed,  in 
great  part,  by  the  mylo-hyoid  muscle,  and  behind  this  by  a 
portion  of  the  hyoglossus  muscle. 

The  parts  exposed  during  the  dissection  of  the  digastric 
space  may  be  classified  according  to  the  subdivision  in 
which  they  lie  : — 


Anterior  Part. 

Posterior  Part. 

1.  Submaxillary  gland. 

2.  Facial  artery  and  vein. 

3.  Hypoglossal  nerve. 

4.  Mylohyoid  nerve. 

5.  Mylo-hyoid  artery. 

6.  Lymphatic  glands. 

1.  Portion  of  the  parotid  gland. 

2.  External  carotid  artery. 

3.  Posterior  auricular  artery. 

The  most  conspicuous  object  in  the  fore-part  of  the  digastric 
triangle  is  the  submaxillary  gland.  The  facial  artery  passes 
first  upwards  and  then  forwards  in  the  midst  of  this  gland, 
whilst  the  facial  vein  lies  superficial  to  it.  But  whilst  the 
facial  artery  runs  through  the  gland,  the  dissector  should 
note  that  it  can  be  separated  from  it  without  any  laceration 
of  the  gland  lobules.  The  gland  is,  as  it  were,  wrapped 
round  it,  so  that,  although  at  first  sight  the  artery  seems  to 
pierce  it,  it  is  in  reality  merely  contained  in  a  deep  furrow  in 
its  substance.  Before  entering  the  gland,  the  facial  artery 
gives  off  its  tonsillitic  and  ascending  palatine  branches,  whilst  its 
submental  and  submaxillary  branches  arise  within  the  gland. 
The  submental  artery  runs  forwards  towards  the  chin.  The 
mylo-hyoid  nerve  and  artery  will  be  seen  passing  forwards  and 
downwards  upon  the  mylo-hyoid  muscle  under  cover  of  the 
submaxillary  gland.  The  twigs  of  the  nerve  to  the  muscle  of 
the  same  name  and  to  the  anterior  belly  of  the  digastric 
should  be  followed  out.  Only  a  very  small  part  of  the  hypo- 
glossal nerve  is  seen  in  this  space.  It  lies  upon  the  hyoglossus 
muscle  immediately  above  the  hyoid  bone,  and  disappears 
under  cover  of  the  posterior  border  of  the  mylo-hyoid  muscle. 
Numerous  small  ly?nphatic  glands  lie  under  shelter  of  the  base 


SIDE  OF  THE  NECK  205 

of  the  lower  jaw.     They  receive  their  afferent  vessels  from 
the  tongue,  teeth,  and  face. 

The  external  carotid  artery  enters  the  posterior  part  of  the 
digastric  triangle.  Here  it  lies  under  cover  of  the  lower  part 
of  the  parotid  gland,  and  gives  off  its  posterior  auricular  branch, 
which  passes  upwards  and  backwards  along  the  upper  border 
of  the  posterior  belly  of  the  digastric  muscle. 

Middle  Line  of  the  Neck. — Before  the  parts  are  further 
disturbed  the  dissector  should  examine  the  structures  which 
occupy  the  middle  line  of  the  neck — a  region,  more  especi- 
ally in  its  lower  part,  of  the  highest  importance  and  interest 
to  the  surgeon.  The  middle  line  of  the  neck  may  be  divided 
by  means  of  the  hyoid  bone  into  an  upper  supra-hyoid  and  a 
lower  infra-hyoid  portion. 

In  the  supra-hyoid  part  are  found  structures  which  are  con- 
cerned in  the  construction  of  the  floor  of  the  mouth.  The 
student  has  already  noticed  that  the  fatty  superficial  fascia  is 
more  fully  developed  here  than  elsewhere  in  the  neck,  and 
that  the  anterior  margins  of  the  two  platysma  muscles  meet 
in  the  mesial  plane  about  half  an  inch  or  so  below  the  chin. 
Above  this  point  their  fibres  decussate.  In  the  present 
condition  of  parts  the  two  anterior  bellies  of  the  digastric 
muscles  are  observed  attached  to  the  mandible  on  either  side 
of  the  symphysis.  From  this  they  descend  towards  the  hyoid 
bone,  and  diverge  slighlty  from  each  other  so  as  to  leave  a 
narrow  triangular  space,  termed  the  submental  triangle,  be- 
tween them  (Fig.  81).  The  floor  of  this  space  is  formed  by 
the  anterior  portions  of  the  two  mylohyoid  muscles,  whilst 
bisecting  the  triangle  in  the  mesial  plane  is  the  fibrous  raphe, 
into  which  these  muscles  are  inserted.  Not  infrequently  the 
inner  margins  of  the  digastric  muscles  send  decussating 
fibres  across  the  interval  between  them.  Within  the  sub- 
mental triangle  are  the  supra-hyoid  glands,  which  lie  above  the 
body  of  the  hyoid  bone  and  are  not  infrequently  the  seat  of 
abscess  following  impetigo  of  the  lower  lip. 

The  infra-hyoid  part  of  the  middle  line  of  the  neck  extends 
from  the  hyoid  bone  to  the  upper  margin  of  the  manubrium 
sterni.  Below  the  hyoid  bone  is  the  thyro-hyoid  membrane 
succeeded  by  the  thyroid  cartilage  with  its  prominent  pomum 
Adami.  Then  comes  the  tense  crico-thyroid  membrane  and 
the  cricoid  cartilage.  Except  along  a  narrow  interval  on 
either  side  of  the  mesial  plane,  these  structures  are  covered 


2o6 


HEAD  AND  NECK 


by  two  muscular  strata,  viz.,  a  superficial  layer  formed  by  the 
sterno-hyoid  and  omo-hyoid  which  lie  on  the  same  plane,  and 
a  deeper  layer  formed  by  the  sterno-thyroid  and  its  continua- 
tion upwards,  the  thyro-hyoid.  In  addition  to  these  an 
elongated   process   of    the    thyroid    gland    not    infrequently 


Anterior  belly  of  digastric 
Mvlo-hvoid 


Submaxillary  gland 


Thyro-hyoid  membrane 


Thyroid  cartilage 

Superior  thyroid  artery 
Crico-thyroid  membrane 

Cricoid  cartila_ 

Lateral  lobe  of  thyroid 
Common  carotid 

Phrenic  nerve 
Inferior  thyroid 
Transversalis  colli 
Vertebral  artery_- 


Anterior  belly  of  digastric 
Mylo-hyoid 


Submaxillary  gland 

Omo-hyoid 
Sterno-hyoid 

Internal  jugular  vein 

Superior  thyroid  vein 

Common  carotid 

artery 

Sterno-mastoid 

Crico-thyroid  muscle 

Lateral  lobe  01 
thyroid  body 
Isthmus  of  thyroid 

Scalenus  anticus 
Scalenus  medius 

Subclavian  artery 


First  rib 


Subclavian  artery 
Suprascapular  artery 

Common  carotid  artery 
Internal  mammary  arte 

Innominate  artery 

Inferior  thyroid  vein 

Fig.  8 i.— Dissection  of  the  Front  of  the  Neck 

sterno-mastoid  muscles  have  been  removed,  and  the  lower  part  of  the 
right  common  carotid  artery  cut  away  to  show  the  deeper  parts. 


The  lower  portions  of  the 


stretches  upwards  (usually  upon  the  left  side),  under  cover  of 
the  sterno-hyoid.  If  this  be  present,  it  will  in  all  probability 
be  observed  to  be  attached  to  the  hyoid  bone  by  a  narrow 
muscular  band  termed  the  levator  glandule  thyroidea.  The 
divergent  inner  margins  of  the  two  small  crico-thyroid 
muscles,  as  they  extend  upwards  and  outwards  upon  the 
cricoid   cartilage   towards   the   lower   margin    of   the   thyroid 


SIDE  OF  THE  NECK  207 

cartilage,  will  also  be  seen.  Upon  the  crico-thyroid  membrane, 
as  it  appears  between  these  muscles,  the  small  crico-thyroid 
artery  runs  transversely  inwards. 

Below  the  cricoid  cartilage  the  dissector  comes  upon  the 
trachea,  which  extends  downwards  through  the  remaining 
portion  of  the  middle  of  the  neck.  As  the  tube  descends  it 
gradually  recedes  from  the  surface,  so  that  at  the  upper 
margin  of  the  sternum  it  lies  very  deeply.  The  length  of 
this  portion  of  the  trachea  varies  with  the  position  of  the 
head.  When  the  chin  is  raised,  and  the  head  thrown  as  far 
back  as  possible,  about  two  inches  and  three-quarters  of  the 
tube  will  be  found  between  the  cricoid  cartilage  and  the 
sternum ;  when,  on  the  other  hand,  the  head  is  held  in  its 
usual  attitude,  the  length  of  the  cervical  part  of  the  trachea 
is  diminished  by  fully  three-quarters  of  an  inch  or  even  more. 
These  measurements  must  be  regarded  as  merely  expressing 
the  average  condition.  They  vary  considerably  in  different 
individuals,  and  are  much  influenced  by  differences  in  the 
length  of  the  neck. 

The  dissector  must  study  carefully  the  parts  which  lie 
superficial,  to  the  trachea  in  this  portion  of  its  course.  In 
the  first  place,  examine  the  structures  which  are  in  immediate 
contact  with  it.  These  are:  (1)  the  isthmus  of  the  thyroid 
body;  (2)  the  inferior  thyroid  veins;  (3)  at  the  root  of  the 
neck,  the  innominate  artery  and  the  left  innominate  vein  ; 
(4)  the  thymus  body  in  young  children  ;  and  (5)  the  occa- 
sional thyroidea  ima  artery.  The  isth?nus  of  the  thyroid  is  a 
thin  band  of  thyroid  substance  which  crosses  the  mesial  plane 
upon  the  anterior  aspect  of  the  trachea.  As  a  general  rule 
it  covers  the  second,  third,  and  fourth  tracheal  rings,  so  that 
only  one  ring  is  left  exposed  between  its  upper  margin  and 
the  cricoid  cartilage.  A  branch  of  the  superior  thyroid 
artery  runs  along  the  upper  margin  of  the  isthmus,  whilst 
upon  its  anterior  surface  is  placed  a  plexiform  arrangement  of 
small  veins.  The  inferior  thyroid  veins  are  two  in  number, 
and  of  large  size.  They  are  formed  by  several  tributaries 
which  issue  from  the  isthmus  and  the  lateral  lobes,  and 
proceed  downwards  upon  the  front  of  the  trachea,  one  upon 
either  side  of  the  mesial  plane.  As  they  descend  they 
frequently  anastomose,  and  the  branches  which  pass  between 
them  may  assume  a  plexiform  arrangement.  Sometimes  the 
two  inferior  thyroid  veins  unite  at  a  variable  point  in  front  of 


2oS  HEAD  .AND  NECK 

the  trachea  into  one  large  trunk.  Close  to  the  sternum  the 
innominate  artery  will  be  observed  lying  upon  the  trachea,  and 
slightly  below  the  level  of  the  upper  border  of  the  bone  the 
left  innominate  vein  crosses  it.  The  thymus  body  in  children 
of  two  years  or  under  is  always  prolonged  upwards  for  some 
distance  into  the  neck  in  front  of  the  trachea.  The  thyroidea 
ima  is  an  occasional  branch  of  the  innominate  artery.  When 
present  it  passes  vertically  upwards  in  front  of  the  trachea  to 
the  isthmus  of  the. thyroid  gland. 

The  parts  which  separate  the  trachea,  with  the  structures 
in  immediate  relation  to  its  anterior  aspect,  from  the  surface 
should  now  be  studied.  The  two  anterior  jugular  veins  as 
they  run  downwards  in  the  superficial  fascia,  one  upon  either 
side  of  the  mesial  plane,  have  been  already  noticed  ;  also, 
the  two  layers  of  the  deep  cervical  fascia  close  to  the  upper 
margin  of  the  sternum,  and  in  the  interval  between  these 
the  cross-branch  connecting  the  two  anterior  jugular  veins. 
Behind  the  fascial  envelope  of  the  neck  come  the  two 
muscular  strata  formed  by  the  sterno-hyoid  and  the  sterno- 
thyroid muscles.  The  inner  margins  of  the  sterno-hyoid 
muscles  are  almost  contiguous  above,  and  held  together  by 
the  fascial  sheaths  which  enclose  them ;  below,  however, 
they  diverge  slightly  from  each  other,  so  as  to  expose,  close 
to  the  sternum,  the  inner  margins  of  the  sterno-thyroid 
muscles.  The  sterno-thyroid  muscles,  in  contact  with  each 
other  below,  gradually  separate  from  each  other  as  they 
ascend.  A  narrow,  lozenge-shaped  space  is  thus  left  between 
the  inner  borders  of  these  muscles.  Over  this  area,  the 
trachea  is  not  covered  by  any  muscular  structure.  Behind 
the  muscles  is  the  pretracheal  layer  of  fascia. 

Surgical  Anatomy. — The  principal  operations  which  are  performed  in 
the  middle  line  of  the  neck  are  those  of  laryngotomy  and  tracheotomy. 

In  laryngotomy,  an  opening  is  made  into  the  larynx.  This  can  most 
readily  be  done  in  the  interval  between  the  thyroid  and  cricoid  cartilages. 
A  vertical  mesial  incision  through  the  integument  is  made  over  this 
interval.  The  crico-thyroid  membrane  is  thus  exposed,  and  is  divided 
transversely  close  to  the  upper  margin  of  the  cricoid  cartilage.  Only  the 
middle  portion  of  the  crico-thyroid  membrane  should  be  divided,  so  as  to 
avoid  injury  to  the  crico-thyroid  muscles. 

Tracheotomy  is  a  more  serious  operation.  The  opening  into  the 
trachea  may  be  made  above  or  below  the  isthmus  of  the  thyroid  body. 
The  high  operation  is  preferred  by  the  surgeon.  Its  advantages  are  very 
apparent  :  here  the  trachea  lies  near  the  surface,  and  no  veins  of  any 
importance  are  met  with.  The  only  drawback  consists  in  the  small 
portion  of  trachea  which  intervenes  between  the  isthmus  and  the  cricoid 


SIDE   OF  THE   NECK  209 

cartilage.  Still,  by  dividing  the  pretracheal  fascia  transversely  below 
its  attachment  to  the  cricoid  cartilage,  the  isthmus  can  be  pushed 
downwards  and  the  interval  between  it  and  the  cricoid  considerably 
increased.  In  certain  cases  it  may  be  necessary  to  divide  the  isthmus, 
and  even  to  open  into  the  lower  part  of  the  larynx  by  extending  the 
incision  through  the  cricoid  cartilage. 

The  loic  operation,  is  a  formidable  undertaking.  It  is  true  that  there  is 
a  greater  length  of  tube  to  be  operated  upon  ;  but  this  is  situated  very 
deeply,  and  the  surgeon  encounters  many  difficulties  before  it  is  reached. 
If  the  dissector  reflect  upon  the  structures  which  intervene  between  this 
part  of  the  trachea  and  the  surface,  he  will  fully  realise  this  ;  and  he  must 
bear  in  mind  that  these  difficulties  are  greatly  intensified  in  the  living 
subject  by  the  engorged  state  of  the  veins,  and  the  convulsive  movements 
of  the  windpipe  as  the  patient  struggles  for  breath.  In  the  child,  the 
thymus  body  interposes  an  additional  obstacle  ;  and  this,  combined  with 
the  more  limited  space,  the  small  calibre  and  great  mobility  of  the  trachea, 
renders  the  operation,  in  such  cases,  a  serious  responsibility.  In  the 
low  operation,  the  trachea  must  be  opened  in  an  upward  direction,  so  as 
to  avoid  injury  to  the  innominate  artery  and  left  innominate  vein,  which 
are  placed  in  front  of  it  at  the  upper  margin  of  the  sternum. 

Infra-hyoid  Muscles. — These  are  a  series  of  fiat,  narrow, 
band-like  muscles  which  lie  upon  the  trachea,  thyroid  body, 
and  larynx.  They  are  disposed  in  two  strata — viz.,  the  omo- 
hyoid and  the  sterno-hyoid  constituting  a  superficial  layer  ; 
and  the  sterno-thyroid  and  thyro-hyoid  a  deep  layer. 

The  omo-hyoid  (musculus  omohyoideus),  as  we  have  noted, 
is  a  two-bellied  muscle.  The  posterior  belly  springs  from  the 
upper  border  of  the  scapula  and  the  suprascapular  ligament. 
It  crosses  the  posterior  triangle  of  the  neck,  so  as  to  divide 
it  into  an  occipital  and  supraclavicular  portion,  and  finally 
terminates  in  the  intermediate  tendon.  This  tendon  lies 
under  cover  of  the  sterno-mastoid  muscle,  and  is  held  in 
position  by  a  strong  process  of  fascia  derived  from  the 
cervical  aponeurosis,  and  firmly  attached  below  to  the 
sternum  and  the  first  costal  cartilage.  The  anterior  belly 
emerges  from  under  cover  of  the  anterior  border  of  the  sterno- 
mastoid,  and  takes  an  almost  vertical  course  through  the 
anterior  triangle.  It  is  inserted  into  the  lower  border  of  the 
body  of  the  hyoid  bone,  close  to  the  outer  side  of  the  sterno- 
hyoid. In  the  anterior  triangle  of  the  neck,  the  anterior 
belly  of  the  omo-hyoid  forms  the  boundary  between  the 
carotid  and  the  muscular  subdivisions  of  this  area.  Both 
bellies  are  supplied  by  branches  from  the  ansa  hypo^Iossi. 

The  sterno-hyoid  (musculus  sternohyoideus)  arises  from  the 
posterior  aspect  of  the  inner  end  of  the  clavicle  and  the 
posterior  sternoclavicular  ligament.      Its  origin,   however,  is 

VOL.   II — 14 


2io  HEAD  AND  NECK 

very  variable ;  thus,  it  may  be  shifted  either  inwards  or  out- 
wards. In  the  former  case,  it  springs  from  the  back  of  the 
manubrium  sterni  and  the  ligament ;  in  the  latter  case,  from 
the  clavicle  alone.  It  is  inserted  into  the  lower  border  of 
the  body  of  the  hyoid  bone,  between  the  mesial  plane  and 
the  insertion  of  the  omo-hyoid.  A  short  distance  above  the 
sternum  an  oblique  fibrous  intersection  frequently  divides  it 
into  two  portions.  The  sterno-hyoid  is  supplied  by  branches 
from  the  ansa  hypoglossi. 

The  sterno-thyroid  (musculus  sternothyreoideus)  lies  under 
cover  of  the  preceding  muscle,  and  is  both  broader  and 
shorter.  It  springs  from  the  posterior  aspect  of  the 
manubrium  sterni  and  from  the  cartilage  of  the  first  rib. 
Diverging  slightly  from  its  neighbour  as  it  ascends,  it  is 
inserted  into  the  oblique  line  on  the  outer  face  of  the  ala  of 
the  thyroid  cartilage.  An  incomplete  tendinous  intersection 
may  sometimes  be  noticed  interrupting  its  muscular  fibres. 
The  nerve  supply  of  the  sterno-thyroid  is  derived  from  the 
ansa  hypoglossi. 

The  thyro-hyoid  (musculus  thyreohyoideus)  lies  on  the 
same  plane  as  the  sterno-thyroid ;  indeed,  it  may  be  regarded 
as  its  continuation  upwards.  It  takes  origin  from  the  oblique 
line  on  the  thyroid  ala,  and  is  inserted  into  the  lower  border 
of  the  body  and  a  part  of  the  great  cornu  of  the  hyoid  bone 
under  cover  of  the  sterno-hyoid  and  omo-hyoid  muscles. 
The  thyro-hyoid  muscle  is  supplied  by  a  delicate  branch 
from  the  hypoglossal  nerve. 

Digastric  Muscle  (musculus  digastricus). — This  muscle 
limits  the  submaxillary  triangle  inferiorly,  and  intervenes 
between  it  and  the  carotid  triangle. 

The  a?iterior  belly  of  the  digastric  springs  from  an  impres- 
sion upon  the  deep  aspect  of  the  base  of  the  mandible,  close 
to  the  symphysis,  whilst  the  posterior  belly  takes  origin  from 
the  digastric  fossa  of  the  temporal  bone  under  cover  of  the 
mastoid  process.  Both  bellies  converge  as  they  proceed 
towards  the  upper  border  of  hyoid  bone,  where  they  are 
joined  by  a  strong  round  intennediate  tendon.  The  posterior 
belly  is  the  longer  of  the  two,  and  is  fusiform  in  shape ;  the 
anterior  belly  is  shorter  and  flatter,  and  descends  in  a  more 
vertical  direction.  The  intermediate  tendon  is  bound  down 
to  the  great  cornu  and  the  body  of  the  hyoid  bone  by  a 
strong  aponeurotic  band.      The  anterior  belly  of  the  digastric 


SIDE  OF  THE  NECK  211 

is  supplied  by  the  ?nylo-kyoid  nerve ;  the  posterior  belly  by  a 
twig  from  the  facial  nerve. 

Stylo-Hyoid  Muscle  (musculus  stylohyoideus). — The  stylo- 
hyoid muscle  lies  along  the  upper  border  of  the  posterior  belly 
of  the  digastric.  It  is  a  small  muscular  band  which  arises  from 
the  posterior  aspect  of  the  styloid  process  of  the  temporal 
bone  not  far  from  its  base.  It  is  generally  inserted  by  two 
slips  into  the  hyoid  bone  at  the  point  where  the  great  cornu 
joins  the  body.  The  intermediate  tendon  of  the  digastric 
passes  forwards  between  the  two  slips  of  insertion  of  the 
stylo-hyoid.  This  muscle  receives  its  nerve  of  supply  from 
the  facial  nerve. 

Hypoglossal  Nerve  (nervus  hypoglossus). — The  portion  of 
the  hypoglossal  nerve  which  traverses  the  anterior  triangle 
can  be  studied  at  this  stage.  It  appears  by  emerging  from 
under  cover  of  the  posterior  belly  of  the  digastric,  and  im- 
mediately curves  forwards  by  hooking  round  the  occipital 
artery.  Near  the  upper  border  of  the  hyoid  bone  it  dis- 
appears from  the  present  dissection  by  passing  under  cover  of 
the  mylo-hyoid  muscle.  It  forms  a  loop  on  the  side  of  the 
neck  which  lies  upon  the  external  carotid  and  lingual  arteries, 
and  finally,  above  the  hyoid  bone,  upon  the  hyoglossus 
muscle.  It  is  crossed  by  the  intermediate  tendon  of  the 
digastric  and  the  two  slips  of  insertion  of  the  stylo-hyoid. 

Two  branches  will  be  seen  to  arise  from  this  portion  of 
the  hypoglossal  nerve,  viz.  : — 

1.  The  ramus  descendens. 

2.  The  thyro-hyoid. 

The  ramus  descendens  hypoglossi,  as  a  rule,  leaves  the  hypo- 
glossal nerve  at  the  point  where  it  turns  round  the  occipital 
artery.  It  proceeds  downwards  and  inwards  so  as  to  cross 
the  common  carotid  artery  very  obliquely.  Reaching  the 
upper  border  of  the  anterior  belly  of  the  omo-hyoid,  it  ends 
by  joining  a  slender  branch  which  advances  towards  it  from 
the  second  and  third  cervical  nerves.  This  nerve  is  called 
the  ramies  cervicalis  descendens,  and  by  its  union  with  the  ramus 
descendens  hypoglossi  a  nerve  loop  is  formed  in  front  of  the 
common  carotid  artery,  which  is  called  the  ansa  hypoglossi. 

From  the  convexity  of  this  loop  branches  are  given  off 
which  supply  both  bellies  of  the  omo-hyoid,  the  sterno-hyoid, 
and  sterno-thyroid  muscles. 


21  2 


HEAD  AND  NECK 


The  branches  for  the  anterior  belly  of  the  omo-hyoid  may 
proceed  from  the  ramus  descendens  hypoglossi  before  it 
reaches  the  ramus  cervicalis  descendens.  The  filament  for 
the  posterior  belly  runs  downwards  and  backwards  along  the 
lower  border  of  the  intermediate  tendon,  and  between  the 
two  laminae  of  the  fascial  sheath  which  retains  the  tendon  in 
position.  The  branch  for  the  sterno-hyoid  and  sterno-thyroid 
muscles  is  a  nerve  which  breaks  up  along  their  outer  margins 
into  a  number  of  twigs  for  their  supply.      One  small  filament 


Joint  capsu 
Joint  cavity-. 


Interarticular 
ligament 

Joint  cavity 


Rhomboid 

ligament 


Anterior 

sterno- 
clavicular 
ligament 


Anterior  chondro- 
sternal  ligament 


Fig.  82. — Sternoclavicular  and  Costo-sternal  Toints. 


may  sometimes  be  traced  into  the  thorax,  where  it  communi- 
cates with  the  phrenic  and  cardiac  nerves. 

The  thyro-hyoid  nerve  is  a  slender  twig  which  comes  off 
from  the  hypoglossal  as  it  approaches  the  hyoid  bone.  It 
supplies  the  thyro-hyoid  muscle. 

Sternoclavicular  Articulation  (articulatio  sterno-clavicu- 
laris). — The  dissector  must  now  examine  the  sterno-clavicular 
joint,  as  the  next  step  consists  in  the  disarticulation  of  the 
clavicle  and  the  reflection  of  the  clavicular  origin  of  the 
sterno-mastoid  muscle. 


SIDE  OF  THE  NECK  213 

The  structures  which  hold  the  two  bones  in  position  at 
this  joint  are  the  following  : — 


Anterior  sternoclavicular. 
Posterior  sterno-clavicular. 


Ligaments  proper.  -! 

A  ,.  .  f  Interclavicular. 

Accessory  ligaments.      4   ^     ,       ,     .     ,  ,        1    •  ■, 

3     &  (  Costo-clavicular  or  rhomboid. 

Interarticular  fibro-cartilage. 

Dissection. — To  expose  these  ligaments  the  origin  of  the  pectoralis 
major  from  the  clavicle  and  the  manubrium  sterni  must  be  removed.  The 
sternal  origin  of  the  sterno-mastoid  is  also,  to  a  certain  extent,  in  the  way, 
but  it  is  not  advisable  to  divide  this. 

Sterno-Clavicular  Ligaments. — These  are  placed  one  in 
front  and  the  other  behind  the  joint,  but  they  are  not  isolated 
sharply  defined  bands.  Above,  they  are  united  by  their 
margins  with  the  interclavicular  ligament,  whilst  below  they 
run  into  each  other  so  as  to  constitute  in  this  manner  a 
capsule  for  the  joint  (capsula  articularis).  The  anterior  sterno- 
clavicular ligament  springs  from  the  front  of  the  inner  end  of 
the  clavicle,  and  proceeds  obliquely  downwards  and  inwards 
to  gain  attachment  to  the  anterior  aspect  of  the  manubrium 
sterni.  The  posterior  sterno-clavicular  ligament  has  a  corre- 
sponding position,  and  presents  similar  attachments  on  the 
posterior  aspect  of  the  joint. 

These  ligaments  limit  the  backward  and  forward  move- 
ments of  the  inner  end  of  the  clavicle,  upon  the  sternal  facet. 

Interclavicular  Ligament  (ligamentum  interclaviculare). — 
This  is  a  strong  band  which  connects  the  inner  ends  of  the 
two  clavicles.  It  is  firmly  fixed  to  the  upper  edge  of  each 
bone,  and  as  it  passes  across  the  middle  line  it  dips  into  the 
notch  on  the  upper  margin  of  the  sternum,  and  is  attached 
to  it  also. 

Rhomboid  Ligament  (ligamentum  costoclaviculare). — The 
costoclavicular  or  rhomboid  ligament  is  composed  of  short 
oblique  fibres.  It  is  placed  behind  the  subclavius  muscle, 
the  remains  of  which  must  therefore  be  removed  to  expose 
its  anterior  surface ;  at  the  same  time  the  clavicle  must  be 
tilted  upwards  as  high  as  possible.  The  rhomboid  ligament 
is  attached  by  its  lower  border  to  the  cartilage  of  the  first  rib. 
From  this  it  is  carried  obliquely  upwards,  backwards,  and  out- 
wards, and  is  fixed  by  its  upper  border  to  a  rough  depression 
upon  the  under  surface  of  the  inner  end  of  the  clavicle. 

The  rhomboid  ligament  plays  an  important  part  in  the 
n—14  a 


2i4  HEAD  AND  NECK 

mechanism  of  the  joint,  and  adds  greatly  to  its  security.  It 
checks  excessive  elevation  of  the  shoulder,  and  restrains, 
within  certain  limits,  both  forward  and  backward  movement 
of  the  clavicle. 

Dissection. — The  interarticular  fibro-cartilage  is  the  most  important  of 
all  the  agents  concerned  in  maintaining  the  apposition  of  the  inner  end  of 
the  clavicle  with  the  sternum.  To  obtain  a  view  of  this  structure,  the 
joint  must  be  opened  into  ;  indeed,  it  is  well  to  remove  as  far  as  possible 
all  the  ligaments.  Begin  by  dividing  the  rhomboid  ligament.  To  effect 
this  the  clavicle  must  be  raised  and  the  knife  carried  inwards  between  its 
inner  end  and  the  first  costal  cartilage.  Next  remove  the  interclavicular 
and  anterior  and  posterior  sterno-clavicular  ligaments.  It  is  difficult  to  get 
at  the  posterior  sterno-clavicular  ligament  in  the  present  condition  of  parts, 
but  with  a  little  care  the  sterno-hyoid  muscle  may  be  detached  from  its  sur- 
face, and  its  fibres  divided.  The  clavicle  should  now  be  forcibly  pulled 
outwards,  when  the  interarticular  fibro-cartilage  will  become  apparent. 

Interarticular  Fibro-Cartilage  (discus  articularis). — This  is 
a  nearly  circular  meniscus  or  plate  interposed  between  the 
inner  end  of  the  clavicle  and  the  sternal  facet.  Its  surfaces 
are  accurately  moulded  upon  both.  As  a  general  rule  it  is 
thicker  around  its  circumference  than  in  the  centre,  where  it 
is  occasionally  perforated.  By  its  circumference  it  is  closely 
attached  to  the  capsule  of  the  joint  both  in  front  and  behind. 
Above,  it  is  firmly  fixed  to  the  upper  edge  of  the  inner  end  of 
the  clavicle ;  below,  its  margin  is  thinned  and  passes  outwards 
under  the  clavicle  to  gain  attachment  to  the  inner  end  of  the 
cartilage  of  the  first  rib. 

The  part  which  the  interarticular  meniscus  plays  in  the 
mechanism  of  the  joint  is  very  apparent.  Its  function  is 
twofold :  (i)  it  acts  as  a  cushion,  and  thus  lessens  the 
shock  of  blows  received  upon  the  shoulder;  (2)  it  acts  as 
a  bond  of  union,  and  prevents  the  clavicle  from  being  driven 
upwards  upon  the  top  of  the  sternum  when  force  is  applied 
to  its  outer  end. 

Synovial  Membranes. — The  sterno-clavicular  joint  is  pro- 
vided with  two  synovial  membranes,  placed  one  upon  either 
side  of  the  interarticular  fibro-cartilage.  These  are  quite 
distinct  from  each  other,  except  in  cases  where  the  fibro- 
cartilage  is  deficient  in  its  centre.  In  the  latter  case  the  two 
synovial  cavities  communicate. 

Dissection. — Complete  the  disarticulation  of  the  clavicle  by  dividing  the 
attachment  of  the  fibro-cartilage  to  the  first  costal  arch.  By  this  step  the 
meniscus  is  removed  with  the  clavicle,  and  can  therefore  be  more  fully 
examined.     Further,  the  clavicular  portion  of  the  sterno-mastoid  can  now 


SIDE  OF  THE  NECK 


215 


be  thrown  forward,  and  the  parts  under  cover  of  this  muscle  dissected. 
The  sternal  origin  of  the  sterno-mastoid  should  not  be  interfered  with  until 
the  subclavian  and  carotid  vessels  have  been  studied. 


Occipital  artery 
Great  occipital  nerve 


Occipital  artery 

External  carotid  artery 
Facial  artery 

.Hypoglossal  nerve 

;      Mi 


Small  occipital  nerve 

Great  auricular  nerve 

Superficial  cervical  nerve 

Spinal  accessory  nerve 

ervical  nerves  to  trapezius  ^ 

Scalenus  amicus 


Lrngual  artery 
Superior  thyroid  artery 
Sterno-hyoid 


ansversalis  colli 

Brachial  nerves 
Suprascapular  artery         / 
Subclavian  artery 

Phrenic  nerve 
Subclavian  vein 

Internal  mammary 


Internal  jugular  vein 
Sterno-hyoid 
Vagus 
Internal  jugular  vein 
Vertebral  vein 
Inferior  thyroid  artery 

Fig.  83. — Dissection  of  the  Posterior  Triangle  of  the  Neck.  The  clavicular 
portion  of  the  sterno-mastoid  has  been  detached  from  the  clavicle  and 
thrown  forwards. 

Certain  structures  at   the  root  of  the   neck    must   now   be   displayed. 
These  are  : — 

1.  The  scalene  muscles. 

2.  The  phrenic  nerve. 

3.  The  subclavian  vessels  and  their  branches. 

4.  The  cervical  pleura. 

5.  The  thoracic  duct  on  the  left  side,  and  the  right  lymphatic  duel  on 

the  right  side. 

6.  The  lower  part  of  the  internal  jugular  vein. 

7.  The  vagus  nerve. 

8.  The  lower  part  of  the  common  carotid  artery. 

9.  The  lower  part  of  the  cervical  sympathetic. 


216  HEAD  AND  NECK 

As  the  dissection  is  proceeded  with,  a  large  number  of  important 
structures  will  be  observed  grouped  in  relation  to  the  scalenus  anticus 
muscle.  Thus  it  is  crossed  in  front  and  from  below  upwards  by — (i)  the 
subclavian  vein,  which  lies  upon  its  insertion  into  the  first  rib  ;  (2)  the 
suprascapular  artery  ;  (3)  the  transversalis  colli  artery  ;  and  (4)  the  omo- 
hyoid muscle,  with  the  nerve  to  its  posterior  belly.  Under  cover  of  these, 
the  phrenic  nerve  is  carried  downwards  upon  the  anterior  aspect  of  the 
muscle,  whilst  the  thoracic  duct  on  the  left  side,  and  the  right  lymphatic 
duct  on  the  right  side,  lie  for  a  short  distance  in  front  of  the  scalenus 
anticus  near  its  inner  margin.  Both  of  these  ducts  open  into  the  venous 
system  at  the  angle  of  union  between  the  internal  jugular  and  subclavian 
veins.  Behind  the  scalenus  anticus,  the  cervical  pleura  bulges  upwards  for 
a  short  distance  into  the  neck,  and  the  subclavian  artery  and  the  brachial 
nerves  are  also  in  relation  to  its  posterior  surface.  Close  to  its  inner 
margin  are  the  thyroid  axis,  the  vertebral  artery  and  vein,  and,  somewhat 
overlapping  it,  the  large  internal  jugular  vein  ;  whilst  ascending  in  the 
interval  between  the  scalenus  anticus  and  the  rectus  capitis  anticus  major 
is  the  small  ascending  cervical  artery. 

Between  the  scalenus  anticus  and  the  trachea  will  be  found  the  internal 
jugular  vein,  the  vagus  nerve,  common  carotid  artery,  the  first  part  of  the 
subclavian  artery  with  its  branches,  and  the  sympathetic  cord. 

This  is  a  tedious  dissection,  on  account  of  the  numerous  twigs  which  are 
given  off  by  the  sympathetic.  Certain  of  these  descend  in  relation  to  the 
first  part  of  the  subclavian  artery,  and  must  be  carefully  preserved.  The 
middle  cervical  ganglion,  as  a  general  rule,  rests  upon  the  inferior  thyroid 
artery,  whilst  the  lowest  ganglion  in  the  neck  is  placed  in,  the  depression 
between  the  transverse  process  of  the  last  cervical  vertebra  and  the  neck 
of  the  first  rib. 

Scalene  Muscles. — These  muscles  constitute  the  fleshy  mass 
which  is  seen  extending  from  the  transverse  processes  of  the 
cervical  vertebrae  to  the  upper  two  costal  arches.  They  are 
three  in  number,  and  are  named,  from  their  relative  positions, 
anticus^  medius,  and  posticus. 

The  scalenus  anticus  (musculus  scalenus  anterior)  is  a  well- 
defined  muscle  which  is  separated  from  the  scalenus  medius  by 
the  brachial  nerves  and  the  subclavian  artery.  It  arises  from 
the  anterior  tubercles  of  the  transverse  processes  of  four  cervical 
vertebras — viz.,  the  third,  fourth,  fifth,  and  sixth, — and,  tapering 
somewhat  as  it  descends,  is  inserted  into  the  scalene  tubercle 
on  the  inner  margin  of  the  first  rib,  and  also  into  the  upper 
surface  of  the  same  bone  between  the  two  subclavian  grooves. 

The  scalenus  medius  (musculus  scalenus  medius)  is  a  more 
powerful  muscle  than  the  preceding.  It  springs  from  the 
posterior  tubercles  of  all  the  cervical  transverse  processes  (with 
the  exception,  in  some  cases,  of  the  first),  and  it  is  inserted 
into  a  rough  oval  impression  which  marks  the  upper  surface 
of  the  first  rib  between  the  tubercle  and  the  groove  for  the 
subclavian  artery. 


SIDE  OF  THE  NECK 


217 


The  scalenus  posticus  (musculus  scalenus  posterior)  is 
generally  inseparable  at  its  origin  from  the  scalenus  medius. 
It  is  the  smallest  of  the  three,  and  springs  by  two  or  three 
slips  from  the  transverse  processes  of  a  corresponding  number 
of  the  lower  cervical  vertebrae  in  common  with  the  scalenus 


Serratus  posticus 
superior  (insertion) 


Scalenus  posticus 
(insertion) 


Scalenus  medius  (insertion) 


Serratus  magnus  (origin) 


Serratus  magnus 
(origin) 


lenus  anticus  (insertion) 


Subclavius 
(origin) 


Pectoralis  minor  (occasional  origin) 


Fig.  84. — Muscle-Attachments  to  the  Upper  Surface  of  the 
First  Rib,  and  the  Outer  Surface  of  the  Second  Rib. 

A,  First  rib  ;  B,  Second  rib. 

medius.  It  is  inserted  into  the  upper  border  of  the  second 
rib,  immediately  in  front  of  the  insertion  of  the  levator  costse. 

The  scalene  muscles  are  supplied  by  twigs  from  the  lower 
four  cervical  nerves. 

Subclavian  Artery  (arteria  subclavia). — The  subclavian 
artery  is  the  first  subdivision  of  the  great  vessel  which  carries 
blood  for  the  supply  of  the  upper  limb.  It  arises  differently 
on  the  two  sides  of  the  body.     On  the  right  side  it  takes  origin 


2l8 


HEAD  AND  NECK 


behind  the  sternoclavicular  articulation  by  the  bifurcation  of 
the  innominate  artery.  On  the  left  side  it  springs,  within  the 
cavity  of  the  thorax,  from  the  aortic  arch.  In  both  cases  it 
takes  an  arched  course  outwards  across  the  root  of  the  neck, 
behind  the  scalenus  anticus  muscle  and  in  front  of  the  cervical 
dome  of  pleura,  a  short  distance  below  its  summit.  At  the 
outer  border  of  the  first  rib  it  enters  the  axilla  and  receives 
the  name  of  axillary  artery. 

The  relations  of  the  subclavian   artery  are   so  numerous, 


Fig.  85. — Diagram  of  the  Subclavian  Artery  and  its 
Branches.      (Turner. ) 


I. 

Innominate  arteiy. 

11. 

Deep  cervical. 

2. 

Common  carotid  artery. 

12. 

Internal  mammary. 

3* 

Vertebral  artery. 

i3- 

Posterior  scapular. 

4- 

Thyroid  axis. 

14. 

Ascending  cervical. 

5- 

Inferior  thyroid  artery. 

a. 

First  rib. 

6. 

Transversalis  colli. 

b. 

Scalenus  anticus. 

7- 

Superficial  cervical. 

c. 

Thyroid  body. 

8. 

Posterior  scapular. 

d. 

Phrenic  nerve. 

9- 

Suprascapular. 

c. 

Vagus  nerve. 

0. 

Superior  intercostal. 

/■ 

Recurrent  laryngec 

and  so  varied  in  character,  at  different  parts  of  its  extent, 
that  it  is  found  necessary  to  subdivide  it  into  three  portions. 
The  first  part  extends  from  the  origin  of  the  vessel  to  the 
inner  margin  of  the  scalenus  anticus ;  the  second  portion  lies 
behind  this  muscle ;  whilst  the  third  part  extends  from  the 
outer  border  of  the  scalenus  anticus  to  the  outer  border  of  the 
first  rib. 

First  part. — Owing  to  the  difference  of  origin,  the  relations 


SIDE  OF  THE  NECK  219 

presented  by  the  first  portion  of  the  subclavian  artery  are  not 
the  same  on  the  two  sides  of  the  body.  Let  us  examine,  in 
the  first  instance,  the  vessel  of  the  right  side,  and  then 
compare  it  with  that  of  the  left  side.  The  first  part  of  the 
right  subclavian  extends  obliquely  upwards  and  outwards,  and 
at  its  termination,  at  the  inner  margin  of  the  scalenus  anticus, 
it  has  reached  a  point  above  the  level  of  the  clavicle.  It  is 
placed  very  deeply.  In  front,  it  is  covered  by  the  skin, 
superficial  fascia,  platysma,  deep  fascia,  and  three  muscular 
strata — viz.,  the  clavicular  origin  of  the  sterno-mastoid,  the 
sterno-hyoid,  and  the  sterno-thyroid.  Three  veins  and  some 
nerves  are  also  placed  in  front  of  it.  Thus,  close  to  the  inner 
margin  of  the  scalenus  anticus,  it  is  crossed  by  the  internal 
jugular  and  vertebral  veins,  as  these  proceed  from  above 
downwards,  whilst  the  anterior  jugular  vein,  as  it  passes  out- 
wards under  cover  of  the  sterno-mastoid,  is  separated  from  it 
by  the  sterno-hyoid  and  sterno-thyroid  muscles.  The  nerves 
which  cross  it  are  the  vagus,  with  the  cardiac  branches  of  the 
vagus  and  sympathetic  as  they  run  towards  the  thorax,  and  a 
loop  from  the  sympathetic  (annulus  Vieusseni).  As  the  vagus 
nerve  leaves  the  artery  it  gives  off  its  recurrent  branch. 

The  first  part  of  the  subclavian  artery  presents  important 
relations  to  the  pleura.  The  cervical  dome  of  this  membrane 
bulges  upwards  behind  it  so  that  the  vessel  rests  upon  its 
anterior  surface  a  short  distance  from  its  summit.  The 
recurrent  laryngeal  branch  of  the  vagus  nerve  hooks  round 
it,  and  is  thus  related  to  it  both  below  and  behind. 

Immediately  below  the  first  part  of  the  subclavian,  and 
upon  a  more  anterior  plane,  the  right  innominate  vein  is 
formed  by  the  union  of  the  internal  jugular  and  subclavian 
trunks. 

On  the  left  side,  the  first  part  of  the  subclavian  ascends 
almost  vertically  from  its  origin  from  the  aortic  arch,  and, 
reaching  the  root  of  the  neck,  it  curves  outwards  upon  the 
pleura  to  gain  the  inner  margin  of  the  scalenus  anticus.  It 
is  only  with  that  portion  of  the  vessel  which  lies  in  the  root 
of  the  neck  that  we  are  concerned  at  present.  Its  relations 
are  somewhat  different  from  those  on  the  right  side.  The 
same  fascial  and  muscular  layers,  and  the  same  nerves  and 
veins,  lie  in  front  of  it.  Owing  to  its  different  direction, 
however,  the  latter  are  placed  more  or  less  parallel  to  it. 
Three    additional    relations    are    established  —  viz.,    (1)    the 


220  HEAD  AND  NECK 

phrenic  nerve,  which  descends  in  front  of  it;  (2)  the  left 
innominate  vein,  which  crosses  it ;  and  (3)  the  thoracic  duct, 
which  first  passes  upwards  in  relation  to  its  inner  or  right 
side,  and  then  arches  over  it  to  reach  the  angle  of  junction 
between  the  subclavian  and  internal  jugular  veins. 

The  recurrent  laryngeal  nerve,  which  on  this  side  hooks 
round  the  arch  of  the  aorta,  lies  to  the  inner  side  of  the 
subclavian  artery. 

Second  part. — The  second  portion  of  the  subclavian  artery 
forms  the  highest  part  or  summit  of  the  arch.  The  average 
height  to  which  the  subclavian  artery  rises  in  the  neck  varies 
from  half  an  inch  to  an  inch  above  the  level  of  the  clavicle. 
In  some  cases,  indeed,  it  may  reach  the  level  of  the  lower 
part  of  the  lateral  lobe  of  the  thyroid  body. 

In  this  part  of  its  course  the  vessel  is  not  so  deeply 
placed.  In  front,  it  is  covered  by — (1)  skin;  (2)  superficial 
fascia  and  platysma ;  (3)  deep  fascia;  (4)  clavicular  head 
of  the  sterno-mastoid ;  (5)  scalenus  anticus.  The  phrenic 
nerve  on  the  right  side  is  also  an  anterior  relation.  It 
passes  downwards  in  front  of  the  vessel,  but  separated  from 
it  by  the  inner  margin  of  the  scalenus  anticus.  Behi?id  and 
below,  the  vessel  is  in  contact  with  the  pleura.  The  sub- 
clavian vein  lies  at  a  lower  level  and  in  front  of  the  artery. 
It  is  separated  from  the  artery  by  the  scalenus  anticus, 
which  intervenes  between  the  two  vessels. 

The  third  part  of  the  subclavian  artery  has  already  been 
examined  (p.  192). 

Branches  of  the  Subclavian  Artery.  —  Four  branches 
spring  from  the  subclavian  trunk  (Figs.  83  and  85).  In  this 
respect,  however,  the  vessel  is  subject  to  considerable  variation. 
They  all  take  origin,  as  a  general  rule,  close  together ;  three 
proceeding  from  the  first  part  of  the  artery  close  to  the 
scalenus  anticus,  and  one  from  the  second  part.  They 
are — 

fi.   Vertebral. 
■p  ,  ( Inferior  thyroid. 

f  \2'   Thyroid  axis.  -  Transversalis  colli. 

jirs  par  .  [Suprascapular. 

V3-   Internal  mammary. 
y  ,         (  ( Superior  intercostal 

seconTpal     j  Superior  intercostal,       .proper. 

r  {  l^Ueep  cervical. 

In  a  great  number  of  cases,  a  branch  of  considerable  size  will  be 
observed  springing  from   the  third  part  of  the  subclavian  artery.     This, 


SIDE  OF  THE  NECK  221 

in  all  probability,  will  be  the  posterior  scapular  artery  arising  directly 
from  the  subclavian.  It  is  so  common  an  occurrence,  that  the  dissector 
must  always  be  prepared  to  meet  it. 

Vertebral  Artery  (arteria  vertebralis). — This  is  the  first 
branch  which  is  given  off  by  the  subclavian.  It  springs 
from  the  posterior  aspect  of  the  trunk  about  a  quarter  of 
an  inch  from  the  inner  margin  of  the  scalenus  anticus  on 
the  right  side,  and  from  the  point  where  the  vessel  reaches 
the  root  of  the  neck  on  the  left  side.  Only  a  small  portion 
of  its  extent  is  seen  in  the  present  dissection.  It  proceeds 
upwards  in  the  interval  between  the  longus  colli  and  the 
scalenus  anticus  muscles,  and  disappears  by  entering  the 
foramen  transversarium  of  the  transverse  process  of  the  sixth 
cervical  vertebra.  It  is  placed  very  deeply,  and  is  covered 
in  front  by  its  companion  vein  and  the  internal  jugular 
vein.      Numerous  large  sympathetic  twigs  accompany  it. 

The  vertebral  artery  on  the  left  side  is  crossed  by  the 
thoracic  duct. 

The  vertebral  vein  will  be  noticed  issuing  from  the 
aperture  in  the  transverse  process  of  the  sixth  cervical 
vertebra.  It  passes  downwards  in  front  of  its  companion 
artery,  and  behind  the  internal  jugular  vein,  to  open  into 
the  posterior  aspect  of  the  commencement  of  the  correspond- 
ing innominate  vein.  Near  its  termination  it  crosses  the 
subclavian  artery.  It  receives  the  deep  cervical  and  the 
anterior  vertebral  veins. 

Thyroid  Axis  (truncus  thyreocervicalis). — This  is  a  short 
wide  trunk,  which  arises  from  the  front  of  the  subclavian 
artery,  close  to  the  inner  margin  of  the  scalenus  anticus, 
and  under  cover  of  the  internal  jugular  vein.  It  lies  between 
the  phrenic  and  pneumogastric  nerves,  and  almost  immediately 
breaks  up  into  its  three  terminal  branches — viz.,  the  inferior 
thyroid,  the  suprascapular,  and  the  transversalis  colli. 

Inferior  Thyroid  Artery  (arteria  thyreoidea  inferior). — 
This  vessel  takes  a  sinuous  course  to  reach  the  thyroid  body. 
At  first,  it  ascends  for  a  short  distance  upon  the  vertebral 
artery,  and  under  cover  of  the  internal  jugular  vein  ;  then, 
at  the  level  of  the  cricoid  cartilage,  it  turns  suddenly  down- 
wards and  inwards,  and  passes  behind  the  sympathetic, 
vagus,  and  the  common  carotid  artery ;  lastly,  it  bends 
upwards,  and  ends  in  branches  at  the  base  of  the  lateral 
lobe  of  the  thyroid  body. 


222  HEAD  AND  NECK 

The  following  branches  will  be  noticed  arising  from  the 
inferior  thyroid  artery  : — 


i.  Ascending  cervical. 

2.  Inferior  laryngeal. 

3.  Tracheal. 


4.  (Esophageal. 

5.  Thyroid. 

6.  Muscular. 


The  ascending  cervical  artery  (arteria  cervicalis  ascendens) 
is  a  small  but  very  constant  vessel,  which  runs  upwards  in 
the  interval  between  the  scalenus  anticus  and  rectus  capitis 
anticus  major,  and  dispenses  branches  to  the  muscles  in 
front  of  the  vertebral  column.  Other  twigs  from  the  ascend- 
ing cervical,  termed  spinal  bra?iches,  enter  the  spinal  canal 
upon  the  spinal  nerves,  and  anastomose  with  branches  from 
the  vertebral  artery.  The  ultimate  distribution  of  the  spinal 
branches  has  already  been  noticed  (p.  158). 

The  inferior  laryngeal  artery  (arteria  laryngea  inferior) 
is  a  small  vessel  which  accompanies  the  recurrent  laryngeal 
nerve  to  the  larynx.  The  tracheal  (rami  tracheales)  and 
(Esophageal  (rami  cesophagei)  branches  in  like  manner  supply 
the  trachea  and  gullet.  They  are  of  small  size,  and  anasto- 
mose with  the  bronchial  and  oesophageal  branches  of  the 
thoracic  aorta.  The  thyroid  or  terminal  branches  (rami 
glandulares)  are  usually  two  in  number.  One  ascends  upon 
the  posterior  aspect  of  the  lateral  lobe  of  the  thyroid  body, 
whilst  the  other  is  given  to  its  base  or  lower  end.  They 
inosculate  with  the  corresponding  vessels  of  the  opposite 
side,  and  also  with  the  branches  of  the  superior  thyroid 
artery.  The  muscular  branches  are  a  series  of  irregular 
twigs  given  to  the  various  muscles  in  the  neighbourhood. 

The  inferior  thyroid  vein  does  not  run  in  company  with 
the  artery  of  the  same  name.  It  is  a  large  vessel  which 
comes  from  the  lateral  lobe  of  the  thyroid  body,  and 
descends  upon  the  trachea  under  cover  of  the  sterno- 
thyroid muscle.  The  veins  of  both  sides  enter  the  thorax, 
and  frequently  unite  to  form  a  short  common  stem,  which 
opens  into  the  innominate  trunk.  In  other  cases,  however, 
the  right  vein  will  be  observed  to  open  separately  into  the 
angle  of  union  between  the  two  innominate  veins.  Both 
veins  receive,  as  they  proceed  downwards,  tributaries  from 
larynx,  trachea,  and  oesophagus. 

The  anterior  vertebral  vein  accompanies  the  ascending 
cervical  artery,  and  opens  into  the  vertebral  vein  as  it  issues 


SIDE  OF  THE  NECK  223 

from  the  foramen  transversarium  of  the  sixth  cervical 
vertebra. 

Suprascapular  and  Transversalis  Colli  Arteries. — Both  of 
these  arteries  have  already  been  examined  in  the  greater  part 
of  their  course  (p.  193).  After  taking  origin  from  the 
thyroid  axis,  they  both  pass  outwards  upon  the  scalenus 
anticus  muscle,  and  under  cover  of  the  clavicular  head  of  the 
sterno-mastoid.  The  suprascapular  (arteria  transversa  scapulae) 
crosses  the  anterior  scalene  muscle  close  to  its  insertion, 
immediately  above  the  subclavian  vein ;  the  transversalis  colli 
(arteria  transversa  colli)  is  placed  at  a  slightly  higher  level. 
Both  vessels  cross  in  front  of  the  phrenic  nerve. 

The  suprascapular  and  transversalis  colli  veins  have  already 
been  seen  joining  the  subclavian  or  the  external  jugular 
vein. 

Internal  Mammary  Artery  (arteria  mammaria  interna). — 
The  internal  mammary  springs  from  the  lower  aspect  of  the  sub- 
clavian opposite  the  thyroid  axis.  It  proceeds  downwards  upon 
the  anterior  surface  of  the  pleura  and  behind  the  inner  end  of 
the  clavicle,  to  reach  the  thoracic  cavity.  In  the  cervical 
part  of  its  course  it  will  be  observed  to  pass  behind  the' 
subclavian  vein,  and  to  be  crossed  from  without  inwards  by 
the  phrenic  nerve.  In  the  neck,  the  internal  mammary 
artery  is  not  accompanied  by  a  companion  vein. 

Superior  Intercostal  Artery  (truncus  costocervicalis). — 
This  branch  takes  origin  from  the  posterior  aspect  of  the 
second  portion  of  the  subclavian  artery,  close  to  the  inner 
border  of  the  scalenus  anticus.  On  the  left  side,  however, 
it,  as  a  rule,  proceeds  from  the  first  part  of  the  parent 
trunk.  To  bring  it  into  view,  the  subclavian  artery  must 
be  dislodged  from  its  position.  It  is  a  short  trunk  which 
passes  upwards  and  backwards  over  the  pleura  to  the  neck 
of  the  first  rib,  where  it  divides  into  the  deep  cervical  artery 
and  the  superior  intercostal  artery  proper. 

The  deep  cervical  artery  (arteria  cervicalis  profunda)  passes 
backwards,  and  disappears  from  view  between  the  transverse 
process  of  the  seventh  cervical  vertebra  and  the  neck  of  the 
first  rib.  It  has  been  already  noticed  in  the  dissection  of 
the  back  of  the  neck  (p.  148). 

The  stiperior  intercostal  artery  (arteria  intercostalis  suprema) 
turns  downwards  in  front  of  the  neck  of  the  first  rib,  between 
the  last  dorsal  nerve  and  the  first  thoracic  ganglion  of  the 


224  HEAD   AND   NECK 

sympathetic,  and  ends  in  the  thorax  by  giving  branches  to 
the  upper  two  intercostal  spaces. 

The  deep  cervical  vein  is  a  large  vessel.  It  joins  the 
vertebral  vein. 

Subclavian  Vein  (vena  subclavia). — The  subclavian  vein 
is  the  continuation  of  the  axillary  vein  into  the  root  of  the 
neck.  It  begins,  therefore,  at  the  outer  border  of  the  first 
rib,  and  arches  inwards  in  front  of  the  scalenus  anticus  muscle 
close  to  its  insertion.  At  the  inner  margin  of  this  muscle, 
and  behind  the  inner  end  of  the  clavicle,  it  joins  the  internal 
jugular  to  form  the  innominate  vein.  In  connexion  with  the 
subclavian  vein,  note:  (i)  that  the  arch  which  it  forms  is  not 
so  pronounced  as  in  the  case  of  the  corresponding  artery ; 
(2)  that  throughout  its  whole  course  it  lies  at  a  lower  level, 
and  upon  a  plane  anterior  to  the  artery;  and  (3)  that  it  is 
separated  from  the  artery  by  the  scalenus  anticus  and  the 
phrenic  nerve. 

The  sheath  of  the  subclavian  vein  is  attached  to  the  posterior  surface  of 
the  costocoracoid  membrane.  This  is  a  relation  of  some  practical  import- 
ance. A  forward  movement  of  the  clavicle  drags  upon  the  vein,  and  in 
cases  where  the  vessel  is  wounded  there  is  always  a  danger  of  air  being 
sucked  into  the  vein  by  such  a  movement.  A  fatal  result  ensues  upon  the 
entrance  of  air  into  the  heart. 

The  tributaries  of  the  subclavian  vein  are  (1)  the  external 
jugular  vein,  and  (2)  in  some  cases  the  anterior  jugular  vein. 
These  join  it  at  the  outer  margin  of  the  scalenus  anticus 
muscle. 

Thoracic  and  Right  Lymphatic  Ducts. — The  thoracic  duct 
(ductus  thoracicus)  is  the  vessel  by  means  of  which  the  lymph 
and  chyle,  derived  from  by  far  the  greater  part  of  the  body, 
are  poured  into  the  venous  system  on  the  left  side  (see  p.  87). 
Its  terminal  or  cervical  portion  is  displayed  in  the  present 
dissection.  It  is  a  small  delicate  vessel,  frequently  mistaken 
for  a  vein,  which  enters  the  root  of  the  neck  upon  the  left 
side  of  the  oesophagus.  It  is  here,  therefore,  that  it  should 
be  sought.  When  it  reaches  the  level  of  the  seventh,  or 
perhaps  the  sixth  cervical  vertebra,  it  changes  its  course  and 
arches  outwards  and  forwards,  and  then  downwards  upon  the 
apex  of  the  pleura,  to  gain  the  outer  margin  of  the  internal 
jugular  vein  at  its  angle  of  union  with  the  subclavian,  and 
into  this  it  opens.  As  the  thoracic  duct  courses  outwards,  it 
is  placed  at  a  higher  level  than  the  subclavian  artery,  and 


SIDE  OF  THE  NECK 


225 


passes  behind  the  internal  jugular  vein.  Further,  as  it  ap- 
proaches the  point  at  which  it  ends,  it  crosses  the  first  part  of 
the  subclavian  artery. 


Stern 

Sym 

Inferior  constrictor 

Thyro 
dragged 


Inferior  thyroid 

artery      1 

Recurrent  laryngea 

nerve 

<  Esophagus 

Common  carotid 
artery 

Internal  jugular  vein 


nferior  thyroid  vein 

Innominate  artery 


ternal 
x         carotid  artery 
Internal  jugular  vein 

Scalenus  medius 

^|^  Rectus  capitis  anticus 
major 

^  Vagus  nerve 
Phrenic  nerve 
ertebrai  vessels 
Scalenus  anticus 
Dome  of  pleura 

Brachial  nerves 

^Subclavian 
vessels 


Suprascapular  and  trans- 
versalis  colli  arteries 
Thoracic  duct 
Pleura 
Internal  mammary  artery  and  phrenic  nerve 

Left  innominate  vein 


FlG.  86. — Deep  Dissection  of  the  Root  of  the  Neck  on  the  Left  Side  to  show 
the  Dome  of  the  Pleura  and  the  relations  of  the  Terminal  Part  of  the 
Thoracic  Duct.  The  sterno-mastoid  and  the  depressors  of  the  hyoid  and 
larynx  have  been  removed. 

A  valve  composed  of  two  segments  guards  its  orifice  into 
the  jugular  vein.  This  allows  its  contents  to  flow  freely  into 
the  vein,  but  acts  as  a  barrier  to  the  passage  of  venous  blood 
into  the  duct. 


vol.  11 — 15 


226  HEAD  AND  NECK 

The  right  lymphatic  duct  (ductus  lymphaticus  dexter)  is  the 
corresponding  vessel  upon  the  right  side.  It  is  a  very  insignifi- 
cant duct,  and  draws  its  supply  of  lymph  from  a  much  more 
restricted  field.  It  is  formed  by  the  union  of  the  lymphatic 
vessels  from  the  right  upper  limb  with  the  right  common 
jugular  lymphatic  trunk.  It  likewise  receives  the  efferent 
lymphatic  vessels  from  the  intercostal  glands  which  lie  in  the 
upper  interspaces  of  the  right  side  and  from  the  thoracic 
visceral  glands  of  the  right  side.  It  constitutes,  therefore, 
the  main  lymphatic  drain  for  the  following  districts  :  (i)  right 
upper  limb;  (2)  right  side  of  the  head  and  neck;  (3)  upper 
part  of  right  thoracic  wall ;  (4)  right  side  of  diaphragm  and 
upper  surface  of  liver;  (5)  thoracic  viscera  on  right  side  of 
mesial  plane,  viz.,  right  side  of  heart  and  pericardium  and  the 
right  lung  and  pleura. 

In  length  the  right  lymphatic  duct  rarely  measures  more 
than  half  an  inch.  It  will  be  found  at  the  inner  margin  of 
the  scalenus  anticus  opening  into  the  angle  of  union  between 
the  internal  jugular  and  subclavian  veins  of  the  right  side. 
As  in  the  case  of  the  thoracic  duct,  its  orifice  is  guarded  by 
a  double  valve. 

Cervical  Pleura. — The  pleural  sac  of  each  side,  with  the 
apex  of  the  corresponding  lung,  projects  upwards  into  the 
root  of  the  neck,  and  the  dissector  should  now  examine  the 
height  to  which  it  rises,  and  the  connections  which  it  estab- 
lishes. Its  height  with  reference  to  the  first  pair  of  costal 
arches  varies  in  different  subjects.  In  some  cases  it  extends 
up  for  two  inches  above  the  sternal  end  of  the  first  rib ;  in 
others  for  not  more  than  one  inch.  These  differences  depend 
on  the  degree  of  obliquity  of  the  thoracic  inlet.  Posteriorly, 
and  in  all  cases,  the  apex  of  the  pleura  will  be  found  to  cor- 
respond in  level  with  the  neck  of  the  first  rib.  It  forms  a 
dome-like  roof  for  each  side  of  the  thoracic  cavity,  and  is 
strengthened  by  a  fascial  expansion  (frequently  termed  Sibson's 
fascia),  which  covers  it  completely,  and  is  attached  on  the 
one  hand  to  the  transverse  process  of  the  seventh  cervical 
vertebra  and  on  the  other  to  the  inner  margin  of  the  first  rib. 
Observe,  further,  that  the  cervical  pleura  is  supported  above 
by  the  scalene  muscles,  under  cover  of  which  it  ascends  into 
the  neck,  and  that  the  subclavian  artery  arches  outwards  upon 
its  anterior  surface  near  its  apex. 

Cervical  Plexus  (plexus  cervicalis) — Fig.  87. — This  plexus 


SIDE  OF  THE  NECK 


227 


is  formed  by  the  anterior  primary  divisions  of  the  upper  four 
cervical  nerves.  These  nerves  are  much  smaller  than  the 
lower  cervical  nerves  which  form  the  brachial  plexus,  and 
they  have  only  a  short  course  to  run  as  independent  trunks. 
With  the  exception  of  the  first,  each  divides  into  an  ascending 
and  a  descending  branch  ;  and  these  joining  with  each  other, 
constitute  the  plexus,  which,  therefore,  consists  of  three  loops. 


Small  occipital  I  " 
R 

Great  auricular, 


Hypoglossal 


Transverse  cervical 


Thyro-hyoid  nerve 
Descendens  hypoglossi 


Branch  to  levator, 
anguli  scapulae 


Branch  to  levator 
anguli  scapula; 


Descending  trunk 


FIG.   87.- 


/'Ansa  hypoglossi 


Phrenic 

-Diagram  of  the  Cervical  Plexus  and  the  Ansa 
Hypoglossi. 


I,  II,  III,  IV. — Anterior  primary  divisions  of  the  upper  four  cervical  nerves. 


R.  Branches  to  recti  muscles. 
S.M.  Branches  to  the  sterno-mastoid. 
C.C.   Rami  communicantes  hypoglossi. 


C.H.  Communicating    branch   to   hypo- 
glossal. 


This  diagram  shows  that  the  descendens  hypoglossi,  the  branch  to  the 
thyro-hyoid,  and  in  all  probability  the  branches  to  the  genio-hyoid,  are 
composed  of  fibres  given  to  the  hypoglossal  by  the  communicating  twigs 
it  receives  from  the  first  cervical  nerve. 


The  descending  branch  of  the  fourth  nerve,  which  is  very 
small,  proceeds  downwards  to  unite  with  the  fifth  nerve,  and 
thus  establishes  a  connexion  with  the  brachial  plexus. 

The  cervical  plexus  thus  formed  has  very  definite  relations. 
It  lies  under  cover  of  the  upper  part  of  the  sterno-mastoid 
and  upon  the  scalenus  medius  and  the  levator  anguli  scapulae 
muscles. 

11 — 15  a 


228 


HEAD  AND  NECK 


Its  branches  are  very  numerous,  and  may  be  classified  in 


the  following  manner 


Superficial  or  ' 
Cutaneous. 


[Ascending. 
-  Transverse. 


.Descending. 


Deep. 


Muscular. 


Communicating. 


From  2nd. 
From  2nd  &  3rd. 

From  3rd  &  4th. 


From  1st  &  2nd. 


From  2nd. 


f  Small  occipital. 

\  Great  auricular. 

Superficial  cervical. 

f  Clavicular. 

J  Sternal. 

I  Acromial. 

r  I.   To     rectus    capitis 

anticus  major. 

To    rectus    capitis 

anticus  minor. 

To    rectus    capitis 

lateralis. 

To  sterno-mastoid. 

Ramus     cervicalis  A 

X  descendens  (rami  I  „         „    ,  c   „    , 

>  •      \  VProm  2nd  &  3rd. 

commumcantes  J 

hypoglossi).  J 

6.  To    levator    angulH 
scapulae. 

7.  To  scalenus  medius  VFrom  3rd  &  4th. 
and  posticus. 

8.  To  trapezius.  J 

9.  Phrenic      to      dia-  \  From     3rd,     4th, 
^  phragm.  J      &  5th. 
f  1.  To  hypoglossal.        j 

2.  To  vagus.  J 

3.  From  sympathetic.  !       «     .2  '   ^ 

4.  To    spinal     acces-/From     2nd,      3rd, 


sory. 


\     &  4th. 


The  superficial  branches  have  already  been  examined  ;  but 
now  that  the  plexus  is  fully  dissected,  the  student  should 
again  study  their  mode  of  origin. 

Muscular  Branches. — The  anterior  recti  muscles  and  the 
rectus  lateralis  receive  twigs  from  the  first  loop  of  the  plexus ; 
but  as  this  is  placed  very  high  up  in  the  neck,  these  branches 
can  only  be  satisfactorily  displayed  in  the  deep  dissection 
of  the  neck.  The  sterno-mastoid  muscle  draws  one  or  more 
twigs  from  the  second  cervical  nerve,  and  by  means  of  these 
a  communication  is  effected  with  the  spinal  accessory  nerve, 
which  pierces,  and  at  the  same  time  supplies  filaments  to  the 
muscle.  The  levator  anguli  scapula  always  receives  two  or 
three  branches  from  the  third  and  fourth  nerves,  whilst  the 
scalenus  medius  and  scalenus  posticus  obtain  their  nerve-supply 
from  the  same  nerve  trunks  before  these  have  entered   the 


SIDE  OF  THE  NECK  229 

plexus.  The  branches  to  the  trapezius  come  off  in  common 
with  the  trunk  which  divides  into  the  descending  superficial 
nerves,  and  are  therefore  derived  from  the  third  and  fourth 
nerves.  Upon  the  under  surface  of  the  trapezius,  these 
branches  unite  with  the  spinal  accessory,  and  form  the  sub- 
trapezial  plexus. 

The  ramus  cervicalis  descendens  is  formed  by  the  union  of 
two  long  slender  roots  (rami  communicantes  hypoglossi)  which 
spring  from  the  second  and  third  nerves  respectively.  It 
proceeds  downwards  and  inwards  under  cover  of  the  sterno- 
mastoid,  and  either  behind  or  in  front  of  the  internal  jugular 
vein,  to  join  the  ramus  descendens  hypoglossi  and  form  the 
ansa  hypoglossi.  In  some  cases  the  twTo  roots  of  the  descen- 
dens cervicalis  remain  separate  throughout  all  their  course. 

The  phrenic  nerve  is  the  most  important  branch  given  off 
by  the  cervical  plexus.  It  springs  from  the  fourth  cervical 
nerve,  and  as  a  rule  obtains  also  a  root  from  the  fifth  or  the 
third  cervical  nerve,  or  perhaps  from  both.  If  the  root  from 
the  fifth  nerve  fails,  the  phrenic  will  in  all  probability  be 
found  to  receive  lower  down  a  twig  from  the  nerve  to  the 
subclavius.  The  course  which  the  phrenic  pursues  in  the 
neck  is  so  definite,  that  there  should  never  be  any  difficulty 
in  recognising  this  nerve.  It  descends,  inclining  at  the  same 
time  inwards,  in  front  of  the  scalenus  anticus,  and  leaves  the 
neck  to  enter  the  thorax  by  passing  under  cover  of  the 
subclavian  vein,  and  crossing  the  internal  mammary  artery 
from  without  inwards.  As  it  proceeds  downwards  on  the 
scalenus  anticus,  it  passes  behind  the  omo-hyoid,  the  trans- 
versalis  colli  artery,  the  suprascapular  artery,  and  on  the  left 
side  the  thoracic  duct. 

The  phrenic  nerve  gives  off  no  branches  in  the  neck,  but 
before  it  enters  the  thorax  it  is  usually  joined  by  a  small 
sympathetic  twig. 

Communicating  Branches. — (1)  At  the  base  of  the  skull, 
the  first  loop  of  the  cervical  plexus  is  brought  into  close 
connexion,  by  means  of  connecting  twigs,  with  the  vagus  and 
hypoglossal  nerves.  These  cannot  be  displayed  at  present, 
but  will  be  examined  in  a  subsequent  dissection. 

The  fibres  which  enter  the  hypoglossal  nerve  from  the  first  cervical 
nerve  proceed  downwards  in  its  trunk  and  conic  off  as  the  descendens 
hypoglossi  The  ansa  hypoglossi  is  thus  in  all  probability  composed 
entirely  of  fibres  derived  from  the  1st,  2nd,  and  3rd  cervical  nerves.      It  is 


230  HEAD  AND  NECK 

also  believed  that  the  branches  which  the  hypoglossal  nerve  gives  to  the 
thyro-hyoid  muscle  and  the  genio-hyoid  muscle  likewise  come  from  the 
1st  cervical  nerve. 

(2)  Each  of  the  four  cervical  nerves  which  form  the 
plexus  is  connected  by  means  of  one  or  more  grey  rami 
communicantes  with  the  superior  cervical  ganglion  of  the 
sympathetic.  (3)  Communications  are  effected  indirectly  in 
two  places  by  the  second,  third,  and  fourth  nerves  with  the 
spinal  accessory,  viz.,  in  the  substance  of  the  sterno-mastoid 
by  the  twig  from  the  second  nerve  to  this  muscle,  and  again 
on  the  under  surface  of  the  trapezius  by  the  branches  which 
go  to  this  muscle  from  the  third  and  fourth  nerves. 

Common  Carotid  Artery  (arteria  carotis  communis). — 
The  common  carotid  is  the  great  artery  of  supply  to  the 
head  and  the  neck.  Its  origin  is  different  on  the  two  sides 
of  the  body.  On  the  right  side,  it  springs  with  the  subclavian 
from  the  innominate  artery  behind  the  upper  part  of  the 
sterno-clavicular  articulation ;  on  the  left  side,  it  arises  within 
the  thorax,  from  the  aortic  arch.  In  both  cases  the  common 
carotid  ends  opposite  the  lower  border  of  the  third  cervical 
vertebra,  or  at  a  level  corresponding  to  the  upper  border  of 
the  thyroid  cartilage  by  dividing  into  the  external -and  internal 
carotid  branches.  The  point  at  which  this  subdivision  takes 
place  is  subject  to  a  considerable  amount  of  variation  within 
certain  limits,  and  it  has  been  noticed  that  in  short-necked 
individuals  the  common  carotid  artery  is  relatively  longer 
than  in  long-necked  people.  The  course  which  the  common 
carotid  arteries  pursue  in  the  neck,  and  the  relations  which 
they  exhibit,  are  so  much  alike  on  the  twro  sides  that  one 
description  will  suffice  for  both. 

The  course  of  the  common  carotid  is  slightly  oblique,  and 
may  be  marked  on  the  surface  by  drawing  a  line  from  the  sterno- 
clavicular articulation  to  a  point  midway  between  the  angle  of 
the  lower  jaw  and  the  mastoid  process.  At  the  root  of  the  neck 
the  two  vessels  are  close  together,  the  trachea  and  oesophagus 
alone  intervening ;  but  as  they  proceed  upwards  they 
diverge  slightly  from  each  other,  and  where  they  end  they 
are  separated  by  the  entire  width  of  the  thyroid  cartilage 
and  the  pharynx. 

Together  with  the  internal  jugular  vein,  the  pneumogastric 
nerve,  and  the  descendens  hypoglossi  nerve,  the  vessel  is 
enveloped   by  a   strongly  marked   sheath    derived   from    the 


SIDE  OF  THE  NECK 


231 


cervical  fascia.  This  has  been  removed,  but  its  constitution, 
and  the  relation  which  its  contents  bear  to  each  other  within 
it,  have  been  already  observed  (pp.  186,  201,  202). 

The  common  carotid  artery  is  very  differently  circum- 
stanced in  regard  to  the  surface  in  its  lower  and  upper  parts. 
Opposite  the  cricoid  cartilage  it  is  crossed  by  the  anterior 
belly  of  the  omo-hyoid,  and  below  this  it  is  placed  very 
deeply,  being  covered  by  the  integument,  platysma,  and  deep 
fascia,  and  by  three  muscular  strata,  viz.,  the  sterno-mastoid, 
the  sterno-hyoid,  and  the  sterno-thyroid. 

Above  the  level  of  the  omo-hyoid  muscle  it  lies  within 
the   limits   of  the   carotid   triangle,    and   is   therefore  placed 


Thyrohyoid  membrane 
True  vocal  cord 
Processus  vocalis 
Arytenoid  cartilage 
Platysma 


Posterior  wall 
of  pharyn 
Retropharyn- 
geal space^ 

Carotid  sheath 


Sterno-hycid 

jfc^.    Thyro-hyoid 

N^      Thyroid  cartilage 
Omo-hyoid 
^%.^C     .Sinus  pyriformis 
-    -  Superior  thyroid 

Descendens 
iV' hypoglossi 
^  ^Common  carotid 


Scalenus  anticu 

Lonarus  colli 


\    9-    ^  \  Internal  jugular 

Kv%VVagus 

Sympathetic  cord 


Vertebral  artery 


Fig.  88. — Transverse  section  through  the  Neck  at  the  level  of  upper 
part  of  Thyroid  Cartilage. 

nearer  the  surface.  Here  it  is  merely  overlapped  by  the 
anterior  margin  of  the  sterno-mastoid  muscle,  and  covered 
by  the  platysma,  fasciae,  and  integument.  The  vessels  and 
nerves  in  relation  to  its  anterior  surface  are : — 

4.  Sterno-mastoid  artery. 

5.  Descendens     hypoglossi    nerve 
and  the  ansa  hypoglossi. 


1.  Superior  thyroid  vein. 

2.  Middle  thyroid  vein. 

3.  Anterior  jugular  vein. 


The  three  veins  cross  the  common  carotid  from  within  out- 
wards, and  at  different  levels,  viz.,  the  superior  thyroid  near  its 
bifurcation,  the  middle  thyroid  below  the  level  of  the  cricoid 
cartilage,  and  the  anterior  jugular  at  the  root  of  the  neck ; 
whilst,  however,  the  thyroid  veins  are  in  immediate  relation 
to  the  vessel,  the  anterior  jugular  vein  is  separated  from  it  by 
the  sterno-hyoid  and  sterno-thyroid  muscles.  The  sterno- 
n—15  6 


2^2 


HEAD  AND  NECK 


mastoid  artery,  a  branch  of  the  superior  thyroid,  crosses  the 
vessel  obliquely  as  it  lies  within  the  carotid  triangle.  The 
ramus  descendens  hypoglossi  proceeds  downwards  and  inwards 
upon  the  vessel,  and  within  its  sheath.  The  ansa  hypoglossi 
is  formed  upon  the  anterior  aspect  of  the  common  carotid 
artery  by  the  union  of  the  ramus  descendens  hypoglossi  with 
the  ramus  descendens  cervicalis. 

Behind,  the  vessel  is  in  apposition  with  the  longus  colli 
and  the  scalenus  anticus  muscles  below,  and  with  the  rectus 
capitis  anticus  major  higher  up.  These  intervene  between  it 
and  the  transverse  processes  of  the  cervical  vertebrae.  The 
gangliated  cord  of  the  sympathetic,   the  recurrent  laryngeal 


Anterior  jugular  vein 
Superior  thyroid  arter-  V 
Pharyny 
Descender! 
hypogloss 
Common  carotic'  v 

Internal  jugulai  N 
Vagus*- 

Sympathetic--, 


Sterno-hyoid    Cric0.thyroid 

^Superior  thyroid  artery 
.Sterno-thyroid 


ens  hypoglossi 
hyoid 
ommon  carotid 
Vagus 

nternal  jugular 
^Sympathetic 

cord 
^Cervical  nerves 


Longus  colli 


Retro-pharyngeal  space       Vertebral  artery 


Fig.  89. —  Transverse  section  through  the  Neck  at  the  level  of  the 
Cricoid  Cartilage. 


nerve,  and  the  inferior  thyroid  artery  are  also  related  to  it 
posteriorly.  The  syjnpathetic  cord  descends  vertically  in  the 
substance  of  the  carotid  sheath,  behind  the  artery,  and  is 
interposed  between  the  vessel  and  the  prevertebral  muscles ; 
the  recurrent  lar)>ngeal  nerve  is  carried  upwards  and  inwards 
behind  the  lower  part  of  the  vessel ;  the  itiferior  thyroid  artery 
crosses  behind  the  carotid  sheath  about  the  level  of  the  sixth 
cervical  vertebra. 

To  the   outer  side  of  the  common  carotid  artery  lie  the 
pneumogastric   nerve   and   the  internal  jugular  vein,1  whilst 


1  On  the  left  side,  at  the  root  of  the  neck,  the  internal  jugular  vein  is 
closely  applied  to  the  artery — so  close  is  it,  indeed,  that  it  may  be  said  to 
overlap  it.  On  the  right  side,  however,  the  vein  is  separated  from  the 
artery  by  a  slight  interval,  through  the  middle  of  which  the  vagus  nerve 
passes  down  perpendicularly. 


SIDE  OF  THE  NECK  233 

internally,  it  is  in  contact  with  a  succession  of  structures  as  it 
proceeds  upwards,  viz.,  (1)  the  trachea  and  cesophagus,  with 
the  recurrent  laryngeal  nerve  in  the  groove  between  them  ; 
(2)  the  lateral  lobe  of  the  thyroid  body,  which  overlaps  the 
vessel ;  (3)  the  larynx  and  the  pharynx. 

As  a  general  rule,  the  common  carotid  artery  gives  off  no 
collateral  branches,  and  its  calibre  is  of  nearly  equal  diameter 
throughout,  except  close  to  its  bifurcation,  where  a  slight 
bulging  or  dilatation  may  usually  be  noticed. 

Carotid  Body. — This  is  a  little  oval  reddish-brown  body, 
placed  upon  the  deep  aspect  of  the  common  carotid  artery 
at  the  point  where  it  bifurcates.  To  expose  it,  therefore, 
the  vessel  must  be  twisted  round  in  such  a  manner  that 
its  posterior  surface  comes  to  look  forwards.  It  is  closely 
connected  with  the  sympathetic  filaments  which  twine 
around  the  carotid  vessels,  and  in  structure  it  is  similar  in 
its  nature  to  the  minute  coccygeal  body  which  rests  upon 
the  anterior  aspect  of  the  tip  of  the  coccyx.  It  is  included, 
therefore,  in  the  group  of  ductless  glands.  Entering  it  are 
numerous  minute  arterial  twigs,  which  take  origin  from  the 
termination  of  the  common  carotid  and  the  commence- 
ment of  the  external  carotid.  The  function  of  this  remark- 
able little  body  is  quite  unknown.  Most  likely  it  is  a 
vestigial  structure. 

External  Carotid  Artery  (arteria  carotis  externa). — The 
external  carotid  artery  commences  at  the  upper  border  of  the 
thyroid  cartilage,  and,  taking  an  upward  course,  it  ends  in 
the  substance  of  the  parotid  gland,  immediately  behind  the 
neck  of  the  lower  jaw,  by  dividing  into  the  superficial 
temporal  and  the  internal  maxillary  arteries.  It  is  termed 
external,  not  on  account  of  its  position  in  relation  to  the 
internal  carotid,  but  on  account  of  its  being  mainly  dis- 
tributed to  parts  on  the  exterior  of  the  skull.  Indeed,  at  its 
origin  its  position  in  relation  to  the  internal  carotid  is  the 
very  reverse  of  that  which  its  name  implies.  It  lies  in  front 
of  the  internal  carotid,  and  somewhat  to  its  inner  side.  As 
it  ascends,  however,  it  inclines  slightly  backwards,  so  that 
very  shortly  it  comes  to  lie  directly  over  the  internal  carotid. 

The  external  carotid  artery  may  be  divided  very  con- 
veniently into  three  stages,  corresponding  to  three  marked 
changes  in  the  relations  which  it  presents.  The  first  stage  is 
contained  within  the  carotid  triangle.      It  is  therefore,  com- 


234 


HEAD  AND   NECK 


paratively  speaking,  superficial.  Here  it  is  overlapped  by 
the  anterior  border  of  the  sterno-mastoid,  covered  by  the 
platysma,  fasciae,  and  integument,  and  crossed  by  the  lingual 
and  common  facial  veins  as  they  run  towards  the  internal 
jugular  vein.  The  second  stage  is  more  deeply  placed.  It 
lies  under  cover  of  the  posterior  belly  of  the  digastric  and 


Superficial 

temporal  artery 

Internal  maxil- 
lary artery 

Posterior  auricu- 

lar  artery  ^j^^S&L. 

•'  ^>     ^ 
External  carotid — 


Occipital  artery 

Sterno-mastoid  artery 

Hypoglossal  nerve 

Ascending  pharyngeal  artery 


Submental 
artery 

Facial  artery 


Internal  carotid  artery 
Descendens  hypoglossi 

Superior  thyroid  artery 
Sterno-mastoid  art 


Lingual  artery 
Inferior  hyoid  artery 

Internal  laryngeal  artery 
Pomum  Adami 


Stemo-hyoid 


Common  carotid  artery 


Omo-hyoid 


Fig.  90. — Diagram  of  the  External  Carotid  Artery  and 
its  Branches. 


the  stylo-hyoid  muscle,  and  is  crossed  by  the  hypoglossal 
nerve.  The  third  stage  is  in  relation  to  the  parotid  gland. 
Emerging  from  under  cover  of  the  digastric  and  stylo-hyoid 
muscles,  the  artery  ascends  for  a  short  distance  under  cover 
of  the  lower  part  of  the  parotid  gland,  and  finally  sinks  into 
its  substance.  Whilst  in  the  parotid  gland,  the  external 
carotid  artery  is  crossed  near  its  termination  by  the  facial 
nerve,  whilst  the  temporo-maxillary  vein  passes  downwards 
superficial  to  it. 


SIDE  OF  THE  NECK  235 

These  relations  cannot  be  seen  at  present,  but  they  will 
afterwards  be  exposed  when  the  face  is  dissected.  It  should 
be  noted  that  while  the  artery  is  in  the  gland  it  lies  much 
nearer  its  deep  than  its  superficial  surface. 

At  its  commencement,  the  external  carotid  artery  lies  in 
relation  to  the  pharynx.  Higher  up  it  rests  upon  the  stylo- 
pharyngeus  muscle,  the  styloid  process,  and  the  glosso- 
pharyngeal nerve — three  structures  which  intervene  between 
it  and  the  internal  carotid  artery. 

As  the  external  carotid  ascends,  it  diminishes  rapidly  in 
calibre,  owing  to  the  numerous  large  branches  which  it  gives 
off. 

It  is  customary  to  classify  these,  according  to  the  direction 
which  they  take,  into  the  following  groups  : — 


Superior  thyroid,  . 

Lingual, 

Facial,  . 

Internal  maxillary, 

Occipital, 

Posterior  auricular, 

Ascending  pharyngeal, 

Superficial  temporal, 


Directed     forwards     and 
inwards. 

\  Directed   backwards  and 
J      outwards. 
Directed  almost  vertically 
upwards. 


But  these  are  not  the  only  branches  which  come  off  from 
the  external  carotid.  Small  twigs  are  also  given  to  the  parotid 
gland,  and  to  the  masseter  and  internal  pterygoid  muscles. 

Superior  Thyroid  Artery  (arteria  thyreoidea  superior). — 
This  vessel  arises  within  the  carotid  triangle,  from  the  fore- 
part of  the  external  carotid  close  to  its  origin.  From  this  it 
takes  a  curved  course  downwards  and  forwards,  under  cover 
of  the  omo-hyoid,  sterno-hyoid,  and  sterno-thyroid  muscles, 
and  ends  by  breaking  up  into  twigs,  which  enter  the  substance 
of  the  thyroid  body. 

The  following  branches  proceed  from  it : — 


1.  Hyoid. 

2.  Superior  laryngeal. 

3.  Sterno-mastoid. 


4.  Crico-thyroid. 

5.  Thyroid. 


The  infra-hyoid  (ramus  hyoideus)  is  a  minute  twig,  which 
springs  from  the  superior  thyroid  before  it  leaves  the  carotid 
triangle,  and  runs  transversely  inwards  under  cover  of  the 
thyro-hyoid  muscle,  and  along  the  lower  border  of  the  hyoid 
bone.  It  anastomoses  with  its  fellow  of  the  opposite  side, 
and  with  the  hyoid  branch  of  the  lingual  artery. 


236  HEAD  AND   NECK 

The  superior  laryngeal  artery  (arteria  laryngea  superior)  is 
a  larger  vessel.  It  springs  from  the  superior  thyroid  as  it 
lies  in  the  carotid  triangle,  and  associating  itself  with  the 
internal  laryngeal  nerve,  it  enters  the  larynx  by  piercing  the 
thyro-hyoid  membrane. 

The  sterno-mastoid  artery  (arteria  sternocleidomastoidea)  is 
a  small  vessel  which  runs  downwards  and  outwards,  along  the 
upper  border  of  the  anterior  belly  of  the  omo-hyoid  muscle, 
and  across  the  carotid  sheath,  to  reach  the  deep  surface  of 
the  sterno-mastoid  muscle,  into  which  it  sinks.  It  gives, 
in  addition,  minute  twigs  to  the  depressor  muscles  of  the 
larynx. 

The  crico -thyroid  artery  (ramus  cricothyreoideus)  runs  in- 
wards upon  the  crico-thyroid  membrane,  and  anastomoses  with 
its  fellow  of  the  opposite  side.  It  has  already  been  noticed 
in  the  dissection  of  the  middle  line  of  the  neck  (p.  207). 

The  thyroid  or  terminal  branches  (rami  glandulares)  of  the 
superior  thyroid  artery  spring  from  the  main  trunk  at  the 
apex  of  the  lateral  lobe  of  the  thyroid  body.  Three  main 
branches  may  be  recognised ;  of  these  the  largest  is  distri- 
buted on  the  posterior  surface  of  the  lateral  lobe ;  the 
smallest  ramifies  on  its  outer  surface ;  whilst  the  third  is 
carried  downwards  upon  the  inner  aspect  of  the  lateral  lobe, 
and  then  along  the  upper  border  of  the  isthmus  towards  its 
fellow  of  the  opposite  side.  The  anastomosis  between  the 
thyroid  arteries  of  the  two  sides  is  by  no  means  free. 

The  superior  thyroid  vein  emerges  from  the  upper  part  of 
the  thyroid  body.  It  receives  tributaries,  which,  in  a  great 
measure,  correspond  with  the  branches  of  the  artery,  and 
crosses  the  upper  part  of  the  common  carotid  to  join  the 
internal  jugular  vein. 

Lingual  Artery  (arteria  lingualis). — Only  a  small  portion 
of  this  artery  is  seen  in  the  present  dissection.  It  springs 
from  the  external  carotid,  a  short  distance  above  the  superior 
thyroid.  In  the  first  instance,  it  takes  an  upward  course, 
but  very  soon  it  changes  its  direction,  and  bends  suddenly 
downwards  to  reach  the  upper  border  of  the  hyoid  bone. 
Here  it  disappears  from  view  by  passing  forwards  under  cover 
of  the  hyoglossus  muscle,  and  it  will  subsequently  be  traced 
to  its  ultimate  distribution  in  the  dissection  of  the  sub- 
maxillary region.  Note  in  the  meantime,  however,  that  the 
part  under  observation  lies  in  the  carotid  triangle,  and  that 


SIDE  OF  THE  NECK  237 

the  loop  which  it  forms  is  crossed  by  the  hypoglossal  nerve. 
One  small  branch,  termed  the  supra-hyoid  artery,  springs  from 
this  part  of  the  vessel. 

The  supra-hyoid  branch  (ramus  hyoideus)  arises  from  the 
lingual,  close  to  the  posterior  margin  of  the  hyoglossus  muscle, 
and  runs  inwards  along  the  upper  margin  of  the  hyoid  bone 
to  anastomose  with  the  corresponding  vessel  of  the  opposite 
side,  and  also  with  the  hyoid  branch  of  the  superior  thyroid. 

Facial  Artery  (arteria  maxillaris  externa). — The  facial 
artery  can  be  studied,  at  the  present  stage  of  the  dissection, 
from  its  origin  up  to  the  point  where  it  mounts  upon  the 
base  of  the  mandible  to  reach  the  face.  This  is  termed  the 
cervical  part  of  the  facial  artery.  It  springs  from  the  fore-part 
of  the  external  carotid,  immediately  above  the  lingual,  and 
then  proceeds  upwards  and  forwards.  Finally,  it  enters  the 
face  at  the  anterior  border  of  the  masseter  muscle  by  passing 
over  the  base  of  the  mandible.  In  its  course  through  the 
neck  it  presents  stages  very  similar  to  those  already  noticed 
in  connection  with  the  external  carotid.  Thus  it  first  lies  in 
the  carotid  triangle,  then  it  disappears  under  cover  of  the 
posterior  belly  of  the  digastric,  the  stylo-hyoid  muscle,  and 
the  hypoglossal  nerve ;  and  finally  it  is  enclosed  within  the 
substance  of  the  submaxillary  gland.  With  regard  to  this 
latter  part  of  the  artery,  it  is  necessary  that  the  dissector 
should  note:  (1)  that  the  vessel  can  be  disengaged  from  the 
submaxillary  gland  by  dissection  without  lacerating  the  gland 
structure ;  it  is  placed,  as  it  were,  in  a  deep  furrow  in  the 
gland  substance ;  (2)  that  in  this  part  of  its  course  it  is 
almost  horizontal,  and  parallel  with  the  lower  margin  of  the 
mandible;  (3)  that  on  emerging  from  the  gland  it  turns 
abruptly  upwards  to  reach  the  face ;  and  (4)  that  the  facial 
vein  passes  backwards  and  downwards  superficial  to  the  sub- 
maxillary gland. 

Four  named  branches  spring  from  the  facial  artery  in  the 
cervical  part  of  its  course  : — 


1.  The  inferior  palatine. 

2.  The  tonsillitic. 


3.  The  submaxillary. 

4.  The  submental. 


The  inferior  palatine  artery  (arteria  palatina  ascendens)  is 
given  off  for  the  supply  of  the  soft  palate,  but  it  also  gives 
branches  to  the  tonsil  nnd  Eustachian  tube.  It  ascends 
between  the  stylopharyngeus  and  styloglossus  muscles.      The 


238  HEAD  AND  NECK 

tonsillitic  artery  (ramus  tonsillaris)  goes  to  the  tonsil,  and  at 
present  is  seen  disappearing  between  the  internal  pterygoid 
and  styloglossus  muscles.  Both  of  these  vessels  will  be 
traced  to  their  destination  in  the  deep  dissection  of  the  neck, 
and  in  the  dissection  of  the  pharynx. 

The  submaxillaiy  branches  are  given  to  the  gland  during 
the  sojourn  of  the  facial  artery  in  its  midst. 

The  submental  artery  (arteria  submentalis)  is  a  branch  of 
some  size.  It  springs  from  the  facial,  close  to  the  base  of 
the  mandible,  and  then  runs  forwards  upon  the  mylo-hyoid 
muscle  towards  the  chin.  Near  the  symphysis  it  changes  its 
direction,  and  is  carried  upwards  over  the  base  of  the  lower 
jaw,  to  end  in  branches  for  the  muscles  and  integument  of 
the  chin  and  lower  lip.  In  the  submaxillary  region  it  gives 
numerous  twigs  to  the  surrounding  muscles  and  glands,  and 
anastomoses  with  the  sublingual  artery  by  branches  which 
pierce  the  mylo-hyoid  muscle.  In  the  face  it  anastomoses 
with  the  inferior  labial  branch  of  the  facial  and  the  mental 
branch  of  the  inferior  dental. 

Facial  Vein  (vena  facialis  anterior). — The  cervical  portion 
of  the  facial  vein  will  be  noticed  passing  backwards  and 
downwards,  superficial  to  the  submaxillary  gland  and  facial 
artery.  After  picking  up  tributaries  corresponding  to  the 
branches  of  the  similar  part  of  the  artery,  it  joins  the  anterior 
division  of  the  temporo-maxillary  vein.  The  short  trunk  thus 
formed  is  termed  the  common  facial  vein,  and  it  pours  its  blood 
into  the  internal  jugular  at  the  level  of  the  hyoid  bone. 

Internal  Maxillary  Artery  (arteria  maxillaris  interna). — 
This  vessel  will  be  displayed  in  the  dissection  of  the  pterygo- 
maxillary  space. 

Occipital  Artery  (arteria  occipitalis). — The  occipital 
artery  springs  from  the  posterior  aspect  of  the  external  carotid 
at  the  same  level  as  the  facial.  It  takes  the  lower  border  of 
the  posterior  belly  of  the  digastric  muscle  as  its  guide,  and 
runs  upwards  and  backwards,  under  cover  of  the  sterno- 
mastoid  muscle,  to  reach  the  interval  between  the  mastoid 
portion  of  the  base  of  the  skull  and  the  transverse  process  of 
the  atlas.  From  this  onwards  it  has  been  studied  in  the 
dissection  of  the  scalp  and  the  back  of  the  neck  (pp.  112 
and  145).  The  first  part  of  the  vessel  crosses  the  internal 
carotid  artery,  the  vagus  nerve,  the  spinal  accessory  nerve,  and 
the  internal  jugular  vein.     The  hypoglossal  nerve  hooks  round 


SIDE  OF  THE  NECK  239 

it,  and  it  is  overlapped  by  the  lower  border  of  the  posterior 
belly  of  the  digastric  muscle. 

The  only  branches  which  spring  from  this  portion  of  the 
occipital  are:  —  (1)  muscular  twigs;  and  (2)  a  meningeal 
branch. 

The  muscular  twigs  (rami  musculares)  are  given  to  the 
neighbouring  muscles,  and  one  of  them,  larger  than  the 
others  and  very  constant,  is  termed  the  sterno-mastoid  branch, 
because  it  associates  itself  with  the  spinal  accessory  nerve, 
and  sinks  with  it  into  the  substance  of  the  sterno-mastoid 
muscle. 

The  meningeal  branch  (ramus  meningeus)  associates  itself 
with  the  internal  jugular  vein,  and  can  be  followed  upwards 
upon  it  to  the  jugular  foramen,  through  which  it  passes  into 
the  cranium. 

Posterior  Auricular  Artery  (arteria  auricularis  posterior). 
— The  posterior  auricular  artery  will  be  found  above  the  level 
of  the  posterior  belly  of  the  digastric,  and,  like  the  occipital, 
it  takes  origin  from  the  hinder  aspect  of  the  external  carotid 
artery.  In  the  first  part  of  its  course  it  is  placed  deeply,  and 
runs  upwards  and  backwards  upon  the  styloid  process  of  the 
temporal  bone  to  reach  the  interval  between  the  mastoid 
process  and  the  back  of  the  auricle.  Here  it  joins  the 
posterior  auricular  nerve,  and  its  further  course  has  been 
studied  in  the  dissection  of  the  scalp  (p.  in).  Before 
gaining  this  point  it  lies  under  cover  of  the  lower  portion  of 
the  parotid  gland. 

This  portion  of  the  posterior  auricular  artery  gives  off — 
(1)  muscular  twigs  ;  (2)  a  few  branches  to  the  parotid  gland ; 
and  (3)  the  stylo-mastoid  artery. 

The  stylomastoid  artery  (arteria  stylomastoidea)  is  a  slender 
vessel  which  enters  the  stylo-mastoid  foramen  upon  the  facial 
nerve.  In  the  interior  of  the  temporal  bone  it  has  an 
extensive  distribution.  It  supplies  twigs  to  the  mastoid  cells 
and  to  the  tympanum,  and  is  carried  onwards  in  the  aqueduct 
of  Fallopius  to  anastomose  with  the  petrosal  branch  of  the 
middle  meningeal. 

Ascending  Pharyngeal  Artery  (arteria  pharyngeaascendens). 
— The  ascending  pharyngeal  artery  is  the  smallest  branch  of 
the  external  carotid.  It  takes  origin  a  short  distance  from 
the  commencement  of  the  parent  trunk,  and  will  be  recognised 
by  its  proceeding   vertically   upwards    between    the    internal 


24o  HEAD   AND  NECK 

carotid   artery   and    the    pharynx.       It   will    be   subsequently 
traced  in  the  deep  dissection  of  the  neck. 

Superficial  Temporal  Artery  (arteria  temporalis  super- 
ficialis). — This  vessel  cannot  be  displayed  at  present.  In  the 
dissection  of  the  face  the  student  will  have  an  opportunity  of 
studying  it. 

Thyroid  Body  (glandula  thyreoidea). — The  thyroid  body 
may  now  be  examined.  It  is  a  highly  vascular  solid  body, 
which  clasps  the  upper  part  of  the  trachea,  and  extends 
upwards  for  some  distance  upon  each  side  of  the  larynx.  In 
size  it  varies  greatly  in  different  individuals,  and  in  females 
and  children  it  is  always  relatively  larger  than  in  adult  males. 
It  consists  of  three  well-marked  subdivisions,  viz.,  two  lateral 
lobes  joined  across  the  middle  line  by  the  isthmus.  Each 
lateral  lobe  is  somewhat  conical  in  form,  its  base  extending 
downwards  as  far  as  the  fifth  or  the  sixth  tracheal  ring,  whilst 
its  apex  rests  upon  the  side  of  the  thyroid  cartilage.  Its 
superficial  surface  is  full  and  rounded,  and  is  clothed  by  the 
pretracheal  layer  of  cervical  fascia,  from  which  it  derives 
a  sheath,  and  also  by  the  sterno-thyroid,  sterno-hyoid,  and 
omo-hyoid  muscles.  It  is  further  overlapped  by  the  sterno- 
mastoid  muscle  (Fig.  89,  p.  232).  Its  deep  surface  is  adapted 
to  the  parts  upon  which  it  lies,  viz.,  to  the  side  of  the  trachea, 
the  cricoid  cartilage,  and  the  thyroid  cartilage ;  whilst  its 
posterior  border  extends  backwards  so  as  to  touch  the  oesophagus 
and  pharynx,  and  overlap  the  common  carotid  artery. 

The  isthmus  of  the  thyroid  body  has  already  been  observed 
in  the  dissection  of  the  middle  line  of  the  neck.  It  is  a 
narrow  band  of  varying  width  which  lies  in  front  of  the  second, 
third,  and  fourth  rings  of  the  trachea,  and  unites  the  bases  or 
lower  ends  of  the  two  lateral  lobes. 

A  still  further  lobe  is  generally  present  in  connexion  with 
the  thyroid  body.  This  is  the  pyramidal  or  the  middle  lobe. 
When  present  it  assumes  the  form  of  an  elongated  slender 
process  which  springs  from  the  isthmus  on  one  or  other  side 
of  the  mesial  plane  (more  usually  on  the  left  side),  and 
extends  upwards  towards  the  hyoid  bone.  To  this  it  may 
be  connected  by  fibrous  tissue,  or  perhaps  by  a  narrow  slip 
composed  of  muscular  fibres,  which  receives  the  name  of 
levator  glandulce  thyreoidea.  In  some  cases  this  little  muscle 
has  an  attachment  to  the  thyroid  body  independently  of  the 
pyramidal  process.      The  thyroid  body  is  firmly  connected  to 


SIDE  OF  THE  NECK 


24 1 


the  parts  upon  which  it  lies,  and  therefore  follows  the  larynx 
in  all  its  movements. 

The  dissector  will  not  fail  to  be  struck  with  the  great  vascularity  of  the 
thyroid  body.  Four  large  arteries,  and  occasionally  a  fifth  smaller  vessel, 
convey  blood  to  its  substance.     The  two  superior  thyroid  branches  of  the 


Anterior  belly  cf  digastric 
Mylohyoid 


Submaxillary  gland 


Thyro-hyoid  membrane 


Thyroid  cartilage 

Superior  thyroid  artery 
Crico-thyroid  membrane 

Cricoid  cartilage 

Lateral  lobe  of  thyroid 

Common  carotid 

Phrenic  nerve 

Inferior  thyroid- 

Transversalis  colli 
Vertebral  artery -L 

Subclavian  artery 
Suprascapular  artery  ^  v 
Common  carotid  artery 
Internal  mammary  artery 

Innominate  artery 
Inferior  thyroid  vein 

Fig.  r;r. — Dissection  of  the  Front  of  the  Neck 


Anterior  belly  of  digastric 
Mylo-hvoid 


>      Submaxillary  gland 


Omo-hyoid 
Sterno-hyroid 

Internal  jugular  vein 
Superior  thyroid  vein 

Common  carotid 
artery 

Sterno -mastoid 

Crico-thyroid  muscle 

Lateral  lobe  of 
thyroid  body 
Isthmus  of  thyroid 

Scalenus  anticus 
Scalenus  medius 
Subclavian  artery 


y  ——First  rib 

Trachea 


The  lower  portions  of  the 
ste;rno-mastoid  muscles  have  been  removed,  and  the  lower  part  cf 
the  right  common  carotid  artery  cut  away  to  show  the  deeper  parts. 

external  carotid  arteries  divide  at  the  apex  of  each  lateral  lobe  into  three 
branches  for  its  supply  ;  the  two  inferior  thyroid  branches  from  the  thyroid 
axis  trunks  of  the  subclavian  arteries  distribute  their  terminal  branches  to 
the  basal  portion  and  deep  surface  of  each  lateral  lobe.  The  occasional 
artery  is  the  thyroidea  ima,  a  branch  of  the  innominate  (more  rarely  of 
the  common  carotid  or  the  aortic  arch),  which  ascends  upon  the  anterior 
aspect  of  the  trachea  to  reach  the  isthmus  of  the  thyroid  body.  These 
thyroid  arteries  anastomose  with  each  other. 

The  veins  which  drain  the  blood  away  from  the  thyroid   body  are  still 
more  numerous.     They  arise  in  part  by  tributaries  which  spring  from  a 

VOL.   II — 16 


242 


HEAD  AND  NECK 


venous  network  on  the  anterior  face  of  the  structure,  but  chiefly  by  branches 
which  emerge  from  its  substance.  They  are  three  in  number  on  each  side 
— viz.,  the  superior  thyroid,  the  middle  thyroid,  and  the  inferior  thyroid. 
The  superior  and  middle  thyroid  veins  cross  the  common  carotid  artery  and 
join  the  internal  jugular  ;  the  inferior  thyroid  descends  in  front  of  the 
trachea.  At  the  root  of  the  neck  it  usually  joins  its  fellow  of  the  opposite 
side  to  form  a  common  stem  which  opens  into  the  left  innominate. 

Trachea  and  the  (Esophagus. — The  windpipe  and  the 
gullet  in  the  cervical  portion  of  their  course  may  now  be 
studied.  Both  begin  at  the  level  of  the  cricoid  cartilage,  in 
front  of  the  sixth  cervical  vertebra.      From  this  point   they 


Thyroid  body 
Trachea 


ommon  carotid  artery 


%  ^0^^^f%l'lr^    •     Inferior  thyroid  artery 

-Jw)     -  >      Recurrent  laryngeal  nerve 


Gullet 


Fig.  92. — Transverse  section  through  the  Thyroid  Body,  Trachea,  and 
Gullet,  at  the  level  of  the  first  Dorsal  Vertebra. 


extend  downwards  in  front  of   the  vertebral  column  to  the 
thoracic  cavity. 

The  trachea,  or  windpipe,  is  a  wide  tube  which  is  kept 
constantly  patent  by  the  cartilaginous  rings  embedded  in  its 
walls.  These  rings  do  not  form  complete  circles ;  posteriorly 
they  are  deficient,  and  in  consequence  the  trachea  is  flattened 
behind.  Above,  it  is  continuous  with  the  larynx,  and 
throughout  its  whole  course  it  is  placed  in  the  mesial  plane 
of  the  body.  The  anterior  relations  of  the  trachea  have 
already  been  fully  discussed  in  connection  with  the  description 
of  the  parts  occupying  the  middle  line  of  the  neck  (p.  207). 
Posteriorly,  it  rests  upon  the  gullet.  Upon  either  side  is  the 
common  carotid  artery;  whilst  closely  applied  to  it  in  its 
upper  part  is  the  lateral  lobe  of  the  thyroid  body.  The 
recurrent  laryngeal  nerve  ascends  on  each  side  in  the  angle 
between  the  trachea  and  oesophagus. 


SIDE  OF  THE  NECK  243 

The  (esophagus  or  gullet  is  a  narrow  tube  with  thick 
muscular  walls,  which  extends  from  the  pharynx  to  the 
stomach.  In  the  cervical  part  of  its  course  it  lies  between 
the  trachea  and  the  prevertebral  muscles,  and  as  it  descends 
it  inclines  slightly  to  the  left,  so  that  it  comes  more  closely 
into  relation  with  the  lateral  lobe  of  the  thyroid  body  and  the 
carotid  sheath  upon  this  side  than  with  the  same  structures 
on  the  opposite  side. 


DISSECTION  OF  THE  FACE. 

The  deep  parts  of  the  neck  cannot  be  displayed  satis- 
factorily until  the  pterygo-maxillary  and  submaxillary  regions 
have  been  opened  up.  It  is  necessary,  therefore,  at  this  stage 
to  leave  the  neck  and  proceed  with  the  dissection  of  the  face. 

Surface  Anatomy  of  the  Ocular  Appendages. — Before  the 
skin  is  reflected  from  the  face,  the  external  anatomy  of  the 
various  appendages  of  the  eye  should  be  studied.  Under 
this  head  we  examine  : — 

1.  The  eyebrows. 

2.  The  eyelids. 

3.  The  conjunctiva. 

The  eyebrows  are  two  curved  tegumentary  projections 
placed  over  the  orbital  arch  of  the  frontal  bone,  so  as  to  inter- 
vene between  the  forehead  above  and  the  ocular  regions 
below.  The  short  stiff  hairs  which  spring  from  these  have  an 
outward  inclination. 

The  eyelids  (palpebrse)  are  two  semilunar  curtains  provided 
for  the  protection  of  each  eyeball.  The  upper  lid  is  the 
longer  and  much  the  more  movable  of  the  two.  When  the 
eye  is  open  the  margins  of  the  two  lids  are  slightly  concave 
and  the  interval  between  them  is  elliptical  in  outline.  This 
interval  is  termed  the  palpebral  fissure  (rima  palpebrarum). 
When  the  eye  is  closed  and  the  margins  of  the  lids  are  in 
apposition  with  each  other,  the  palpebral  fissure  is  reduced 
to  a  nearly  horizontal  line.  Owing  to  the  greater  length 
and  freer  mobility  of  the  upper  lid,  the  fissure  in  this  con- 
dition is  placed  below  the  level  of  the  cornea  or  clear  part  of 
the  eyeball, 
ir— 16a 


244 


HEAD  AND  NECK 


At  the  extremities  of  the  palpebral  fissure  the  eyelids 
meet  and  form  the  palpebral  commissures  or  canthi,  and  at  the 
inner  canthus  the  fissure  expands  into  a  small  triangular  space 
called  the  lacus  lachry mails.  If  the  dissector  now  examine 
the  free  margins  of  the  lids  he  will  observe  that  to  the  outer 
side  of  the  lacus  lachrymalis  they  are  flat,  and  that  in  each 
case   the  eyelashes   project  from    the  anterior  border,   whilst 


Margin  of  the  upper  eye- 
!id  with  openings  of 
Meibomian  ducts 


Papilla  lachrymalis  with 
ounctum  lachrymale  on 
the  summit 


Plica  semilunaris 

Caruncula  lachrymalis 
Papilla  lachrymalis 

Meibomian  openings 


Meibomian  glands 
shining  through  the 
conjunctiva 


Fig.  93. — Eyelid  slightly  everted  to  show  the  Conjunctiva  (enlarged). 


the  Meibomian  follicles  open  along  the  posterior  border, — a 
distinct  interval  intervening  between  the  cilia  and  the  gland- 
mouths.  The  small  portion  of  the  margin  of  each  eyelid,  on 
the  other  hand,  which  bounds  the  lacus  lachrymalis  is  more 
horizontal  in  direction,  somewhat  rounded,  and  destitute  both 
of  eyelashes  and  Meibomian  follicles.  At  the  very  point 
where  the  eyelashes  in  each  eyelid  cease,  and  the  palpebral 
margin  becomes  rounded,  a  minute  eminence  with  a  central 
perforation  will  be  seen.      The  eminence  is  the  papilla  lachry- 


DISSECTION  OF  THE  FACE  245 

ma/is,  whilst  the  perforation,  called  the  punctum  lachrymale^  is 
the  mouth  of  the  lachrymal  canal,  the  duct  which  conveys 
away  the  tears.  Endeavour  to  pass  a  bristle  into  each  of  the 
orifices.  The  upper  canal  at  first  for  a  short  distance  ascends, 
whilst  the  lower  one  descends,  and  then  both  run  inwards  to 
the  lachrymal  sac. 

The  conjunctiva  is  the  membrane  which  lines  the  deep 
surface  of  both  the  lids,  and  is  reflected  from  them  on  to  the 
anterior  aspect  of  the  eyeball.  At  the  margins  of  the  lids  it 
is  continuous  with  the  skin,  whilst  through  the  puncta  lachry- 
malia  and  the  lachrymal  canals  it  becomes  continuous  with 
the  lining  membrane  of  the  lachrymal  sac.  The  line  of  re- 
flection of  the  conjunctiva  from  the  lids  on  to  the  eyeball  is 
termed  the  fornix  conjunctiva.  Owing  to  the  greater  depth  of 
the  upper  lid  the  conjunctival  recess  between  the  upper  lid 
and  the  eyeball  is  of  greater  extent  than  that  in  connexion 
with  the  lower  lid.  The  connexion  between  the  conjunctiva 
on  the  one  hand,  and  the  eyelids  and  sclerotic  coat  of  the 
eyeball  on  the  other,  is  of  a  loose  character.  Over  the  cornea, 
however,  the  membrane  becomes  thinned  down  to  a  mere 
epithelial  covering,  which  is  closely  adherent. 

In  connexion  with  the  conjunctiva  the  plica  semilunaris 
and  the  caruncula  lachrytnalis  must  be  examined.  The 
caruncula  is  the  reddish  fleshy-looking  elevation  which 
occupies  the  centre  of  the  lacus  lachrymalis  at  the  inner 
canthus.  From  its  surface  a  few  minute  hairs  project  The 
plica  semilunaris  is  of  interest  because  in  the  human  eye  it  is 
the  rudimentary  representative  of  the  membrana  nictitans,  or 
third  eyelid,  found  in  many  animals.  It  is  a  small  vertical 
fold  of  conjunctiva,  which  is  placed  immediately  to  the  outer 
side  of  the  caruncula,  and  it  slightly  overlaps  the  eyeball 
at  this  point. 

Dissection. — The  dissection  of  the  face  is  both  difficult  and  tedious. 
The  ramifications  of  the  nerves  are  so  intricate,  and  the  fibres  of  the  facial 
muscles  are  so  pale,  and  so  closely  surrounded  by  the  soft  subcutaneous  fat 
of  the  region,  that  great  care  and  patience  are  required  on  the  part  of  the 
Student  to  obtain  a  propel  display  of  the  various  structures.  In  cases 
where  the  dissection  is  undertaken  for  the  first  time,  it  may  be  well  to 
devote  particular  attention  to  the  nerves  and  muscles  on  tin-  one  side,  and 
to  the  vessels  and  muscles  on  I  lie  opposite  side.  At  the  same  time  it  must 
be  clearly  understood  that  a  good  dissector  should  be  able  to  make  a  com- 
plete dissection  upon  both  sides. 

It  will  facilitate  the  dissection  if  the  student  introduce  under  the  eyelids, 
cheeks,  and  lips  a  small  quantity  of  cotton- wadding  or  tow  soaked  in  spirit. 


246  HEAD  AND  NECK 

The  margins  of  the  lips  may  then  be  stitched  together.  In  doing  this  it  is 
necessary  to  employ  a  fine  needle.  Only  one  incisionals  required  for  the 
reflection  of  the  skin — viz.,  a  vertical  cut  carried  upwards  immediately  in 
front  of  the  ear  until  it  meets  the  coronal  incision  which  was  made  in 
reflecting  the  integument  from  the  scalp.  The  skin  may  then  be  thrown 
forwards  as  far  as  the  middle  line  of  the  face  and  removed  entirely. 

In  raising  the  skin  the  dissector  must  proceed  with  caution.  Carefully 
preserve  the  fibres  of  the  platysma,  as  they  pass  upwards  upon  the  lower 
jaw  to  blend  with  the  fascia,  to  find  insertion  into  the  bone  and  mix  with 
the  fibres  of  certain  of  the  facial  muscles  (p.  180).  The  little  risorius 
muscle  as  it  passes  forwards  from  the  masseteric  region  to  the  angle  of  the 
mouth  is  apt  to  be  injured,  and  must  therefore  be  remembered.  In  the 
case  of  the  eyelids  the  skin  is  thin  and  is  separated  from  the  subjacent 
muscular  fibres  by  a  small  amount  of  areolar  tissue  devoid  of  fat.  Some 
care  therefore  is  required  on  the  part  of  the  dissector  to  remove  it  success- 
fully. Over  the  ala  of  the  nose  and  the  chin,  the  integument  is  difficult  to 
raise  on  account  of  its  density  and  also  from  its  close  connexion  with 
subjacent  structures. 

When  the  skin  is  completely  reflected,  and  the  attachments  of  the 
platysma  satisfactorily  demonstrated,  the  latter  may  be  turned  up  so  as  to 
expose  the  facial  artery  passing  upwards  upon  the  jaw. 

Facial  Branch  of  the  Great  Auricular  Nerve. — The  branch 
which  the  great  auricular  nerve  gives  to  the  face  should  be 
traced  forwards  on  the  cheek.  Several  small  filaments  from 
this  will  be  seen  to  penetrate  the  parotid  gland,  for  the 
purpose  of  joining  the  facial  nerve.  Others  proceed  forwards, 
and  supply  the  skin  over  the  parotid,  masseteric,  and  buccal 
regions. 

Dissection. — The  parotid  gland  should  now  be  defined.  In  doing  this 
the  greatest  care  must  be  taken  not  to  injure  the  branches  of  the  facial 
nerve  and  the  transverse  facial  artery,  as  they  emerge  from  its  substance, 
along  its  upper  and  anterior  borders.  The  duct  also,  which  appears  at  its 
anterior  border,  must  be  followed  forwards  upon  the  masseter  muscle. 
When  the  superficial  relations  of  the  parotid  have  been  examined,  the 
gland-substance  must  be  removed  piecemeal,  so  as  to  bring  into  view  the 
various  structures  with  which  its  deep  surface  is  in  contact,  and  at  the 
same  time  expose  the  blood  vessels  and  nerves  which  traverse  it.  This  can 
best  be  effected  by  tracing  into  it  the  branches  of  the  facial  nerve,  and  the 
trunk  of  the  transverse  facial  artery.  Care  must  be  taken  not  to  injure  the 
auriculo-temporal  nerve,  which  ascends  under  cover  of  the  upper  part  of 
its  posterior  border.  The  communicating  twigs  from  the  auriculo-temporal 
and  great  auricular  nerves  to  the  facial  nerve  must  be  preserved.  By  this 
dissection  the  termination  of  the  external  carotid  artery  and  the  temporo- 
maxillary  vein  will  be  displayed. 

Parotid  Gland  (glandula  parotis). — The  parotid  is  the 
largest  of  the  salivary  glands.  It  is  lodged  in  the  niche  or 
recess  between  the  lower  jaw  and  the  ear,  and  being  adapted 
to  this  recess,  it  presents  an  irregular  figure.  Above,  it  is 
limited  by  the  zygoma.     Below,  its  lower  border  overlaps  the 


DISSECTION  OF  THE  FACE 


247 


posterior  belly  of  the  digastric  muscle,  and  is  separated  from 
the  submaxillary  gland  by  that  partition  of  the  deep  cervical 
fascia  which  the  student  has  already  studied  under  the  name 
of  the  stylo-maxillary  ligament.  Behind,  it  abuts  against  the 
auditory  meatus,  the  mastoid  process,  and  the  sterno-mastoid 
muscle.  In  fronts  it  rests  against  the  posterior  border  of  the 
masseter,  the  posterior  margin  of  the  ramus  of  the  lower  jaw, 


Parotid  duct 


Lower  jaw 

Wharton's  1 
Mucous  me 

Sublingual 


Internal  pterygoid 


Lingual  nerve 

Lower  jaw 
Mylo-hyoid 
Surface  of  submaxil- 
lary gland  covered 
by  mandible 
Surface  covered  by 
intesfument  and  fascia; 


Mylo-hyoid' 
Anterior  belly  of  digastric' 

Fig    94. — Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands. 

and  the  posterior  border  of  the  internal  pterygoid  muscle. 
From  this  aspect  of  the  gland  a  thin  and  somewhat  triangular 
portion  of  the  gland  termed  the  facial  process  is  prolonged 
forwards  for  some  distance  upon  the  surface  of  the  masseter 
muscle.  It  is  from  the  anterior  margin  of  the  facial  process 
towards  its  upper  part  that  the  duct  of  the  gland  emerges,  and 
frequently  a  small  detached  lobule  of  gland  substance  will  be 
observed  lying  upon  the  masseter  in  relation  to  the  upper 
aspect  of  the'  duct  (Fig.  94).  This  is  termed  the  soda 
n— 1Gb 


248 


HEAD  AND  NECK 


parotidis.  The  supe7'ficial  or  external  surface  of  the  parotid  is 
slightly  convex,  and  is  covered  by  the  dense  parotid  fascia 
which  the  dissector  has  already  observed  to  be  a  prolongation 
upwards  into  the  face  of  a  portion  of  the  deep  cervical  fascia 
(p.  185).  In  relation  to  this  surface,  and  under  cover  of  the 
fascia,  there  are  usually  one  or  two  small  lymphatic  glands. 


Levator  labii  superioris 

Antrum  of  Highmore 
Zygomaticus  major 

Buccinator  muscle 
Temporal  muscle 

Tonsil 

Mandibular  vessels 
and  nerve 

Pharynx 

Stylo-pharyngeus 

Stylo-glossus 

ternal  carotid 
Sympathetic 


12      34567 


Fig.  95. — Transverse  section  through  the  Head  at  the  level  of  the  Hard 
Palate.      It  shows  the  relations  of  the  parotid  gland,  etc. 


1.  Temporo-maxillary  vein. 

2.  Sterno-mastoid  muscle. 

3.  Digastric  (posterior  belly). 

4.  Spinal  accessory  nerve. 


5.  Internal  jugular  vein. 

6.  Stylo-hyoid. 

7.  Glosso-pharyngeal  nerve. 

8.  Vagus  and  hypoglossal  nerves. 


The  deep  surface  of  the  gland  is  in  relation  to  many 
important  structures,  and  is  moulded  upon  the  various  parts 
with  which  it  is  in  contact. 

It  rests  upon  the  styloid  process  and  the  muscles  which 
proceed  from  it,  and  is  closely  related  to  the  internal  jugular 
vein  and  the  vagus,  spinal  accessory,  and  hypoglossal  nerves.  A 
portion  of  the  gland  substance  (sometimes  called  the  glenoid  lobe) 
occupies  the  posterior  or  tympanic  part  of  the  glenoid  fossa. 


DISSECTION  OF  THE  FACE  249 

The  fascial  connexions  of  the  parotid  gland  deserve  some 
attention.  The  recess  in  which  it  lies  is  lined  by  a  well- 
marked  fascia,  which  separates  it  from  subjacent  structures, 
and  we  have  noted  the  parotid  fascia  upon  its  superficial 
aspect.  The  entire  gland  is  enveloped,  therefore,  in  a  strong 
envelope,  which  sends  numerous  strong  septa  into  its  sub- 
stance, and  accentuates  its  lobular  appearance.  The  parotid 
fascia  presents  very  important  connexions.  Above,  it  is 
attached  to  the  zygoma ;  behind,  it  is  attached  to  the  meatus 
auditorius,  and  below  that,  it  splits  to  enclose  the  sterno- 
mastoid ;  in  front,  it  is  continuous  with  the  fascia  over  the 
masseter ;  whilst  below,  it  is  continuous  with  the  deep  cervical 
fascia.  The  front  wall  of  this  sheath  in  its  lower  part  is 
thickened  so  as  to  form  the  stylo-maxillary  ligament.  This 
fascial  band  intervenes  between  the  parotid  gland  on  the  one 
hand  and  the  internal  pterygoid  muscle  and  a  small  part  of 
the  submaxillary  gland  on  the  other. 

Parotid  Duct  (ductus  parotideus). — This  is  also  called 
Stensoiis  duct.  It  issues  from  the  anterior  border  of  the 
gland,  and  proceeds  forwards  upon  the  masseter  muscle 
about  half  an  inch  below  the  zygoma.  In  relation  to  it 
above  will  be  seen  the  socia  parotidis  and  the  transverse 
facial  artery,  whilst  accompanying  it  are  some  branches  of  the 
facial  nerve.  At  the  anterior  border  of  the  masseter,  it  turns 
abruptly  inwards  through  the  soft  fat  of  the.  cheek,  and,  pierc- 
ing the  buccinator  muscle,  runs  forwards  for  a  short  distance 
between  this  muscle  and  the  mucous  membrane.  Finally,  at 
a  point  corresponding  with  the  second  molar  tooth  of  the 
upper  jaw,  it  opens  into  the  mouth  by  a  minute  orifice  placed 
on  the  summit  of  a  small  papilla.  In  length,  the  duct 
measures  about  two  inches,  and  its  course  may  be  marked 
out  on  the  surface  of  the  cheek  by  drawing  a  line  from  the 
lower  part  of  the  external  auditory  meatus  of  the  auricle  to  a 
point  mid-way  between  the  nostrils  and  the  margin  of  the  red 
part  of  the  lip.  The  dissector  should  now  open  the  duct, 
and  pass  a  fine  probe  through  it  into  the  mouth.  The 
calibre  of  the  tube  will  then  be  observed  to  be  greatly 
reduced  at  its  opening  upon  the  inner  aspect  of  the  cheek. 
Evert  the  cheek,  and  examine  this  orifice. 

Dissection. — The  parotid  gland  should  now  be  removed  piecemeal  by 
following  the  various  nerves  anrl  vessels  which  traverse  it  through  its 
substance. 


25° 


HEAD  AND  NECK 


Vessels  and  Nerves  which  traverse  the  Parotid. — By  the 
removal  of  the  gland,  the  vessels  and  nerves  which  traverse 
the  gland  are  brought  into  view.      These  are : — 


Superficial 
temporal  arteries 

Temporal  branch 
of  orbital  nerve 
Auriculotemporal 
nerve 


Parotid 


Internal  carotid  — 

External  carotid 

External  jugular  vein 

Superficial 

cervical  nerve 

Descendens 

cervicalis 

Sterno-mastoid 


Parotid  duct 
ansverse  facial 


Masseter 
Facial  artery  and  vein 
Submaxillary  gland 

Hypoglossal  nerve 
Lingual  artery 

Superior  thyroid  artery 


Thyro-hyoid  muscle 
Ansa  hypoglossi  , 

Fig.  96.  — Dissection  of  the  Parotid  Region  and  the  upper  part  of  the 
Anterior  Triansfle  of  the  Neck. 


External  carotid  artery,   f  Superficial  temporal. 

dividing  into     .         .    ^  Internal  maxillary. 
Transverse  facial  artery. 
Temporo-maxillary  vein. 
Facial  nerve,  or  the  seventh  cranial  nerve. 
Communicating  twigs  from  the  great  auricular  and  auriculo-temporal 


nerves  to  the  facial  nerve. 


DISSECTION  OF  THE  FACE  251 

The  external  carotid  (arteria  carotis  externa),  as  it  ascends 
in  the  substance  of  the  gland,  lies  nearer  its  deep  than  its 
superficial  surface.  In  fact,  in  the  lower  part  of  its  parotid 
stage  the  artery  is  not  placed  within  the  gland,  but  merely  in 
a  groove  on  its  deep  surface,  and  slightly  under  shelter  of  the 
posterior  border  of  the  ascending  ramus  of  the  lower  jaw. 
Note  that  the  facial  nerve  crosses  superficial  to  it,  and  that 
opposite  the  neck  of  the  lower  jaw  the  vessel  divides  into  the 
superficial  temporal  and  the  internal  maxillary  arteries. 

The  internal  maxillaty  artery  at  once  passes  forwards 
under  cover  of  the  neck  of  the  jaw  and  disappears  from 
view.  The  superficial  temporal  artery  may  now  be  fully 
followed  out. 

The  temporo-maxillary  vein  is  formed  by  the  union  of  the 
superficial  temporal  and  internal  maxillary  veins  behind  the 
neck  of  the  lower  jaw.  It  descends  in  the  substance  of 
the  parotid  superficial  to  the  external  carotid  artery.  At  the 
lower  border  of  the  gland  it  divides  into  an  anterior  and 
posterior  trunk.  The  former  joins  the  facial  vein,  whilst  the 
latter  unites  with  the  posterior  auricular  vein  to  form  the 
external  jugular. 

Superficial  Temporal  Artery  (arteria  temporalis  super- 
ficialis). — The  superficial  temporal  artery  appears  to  be  the 
direct  continuation  upwards  of  the  external  carotid  artery. 
At  first  in  the  substance  of  the  parotid,  it  soon  emerges  from 
this,  and,  crossing  the  root  of  the  zygoma,  ascends  upon  the 
temporal  fascia  for  a  variable  distance,  and  then  divides  into 
its  two  terminal  branches,  the  anterior  (ramus  frontalis)  and 
posterior  superficial  temporal  (ramus  parietalis)  arteries.  These 
are  described  on  p.  in.  The  superficial  temporal  artery  is 
closely  accompanied  by  the  auriculo-temporal  nerve  and  the 
superficial  temporal  vein. 

In  addition  to  its  terminal  branches  it  gives  off — 


1.  Parotid  twigs. 

2.  Anterior  auricular  branches. 

3.  The  transverse  facial. 


4.  The  middle  temporal. 

5.  The  orbital. 


The  anterior  auricular  branches  (rami  auriculares  anteriores) 
supply  the  anterior  aspect  of  the  external  auricle  and  anasto- 
mose with  the  posterior  auricular  artery. 

The  transverse  facial  (arteria  transversa  faciei)  is  given  off 
in  the  substance  of  the  parotid.     It  runs  transversely  forwards, 


25 2  HEAD  AND  NECK 

and,  emerging  from  under  cover  of  the  anterior  border  of  the 
gland,  proceeds  onwards  across  the  masseter  between  the 
zygoma  and  Stenson's  duct  to  end  in  twigs  which  anastomose 
with  branches  of  the  facial,  buccal,  and  infra-orbital  arteries. 

The  middle  temporal  (arteria  temporalis  media)  arises 
immediately  above  the  zygoma,  and  it  pierces  the  temporal 
fascia  to  reach  the  temporal  muscle  and  communicate  with  the 
deep  temporal  branches  of  the  internal  maxillary  artery. 

The  orbital  artery  (arteria  zygomatico-orbitalis)  is  an  in- 
constant branch  which  runs  forwards  above  the  zygoma 
between  the  two  layers  of  the  temporal  fascia  to  supply  the 
outer  part  of  the  orbicularis  palpebrarum,  and  the  skin  in 
this  neighbourhood. 

Muscles  of  the  Face.  — The  muscles  of  the  face  are 
arranged  in  groups  around  the  different  facial  apertures. 
There  is  thus  a  palpebral  and  superciliary  group  in  relation  to 
each  orbital  opening ;  an  oral  groip  around  the  mouth  ;  and 
a  ?iasal  group  in  connexion  with  the  nose.  Each  of  these 
groups  may  be  examined  in  turn.  It  is  convenient  to  begin 
wTith  the  palpebral  and  superciliary  muscles.  These  are  three 
in  number : — 

1.  Orbicularis  palpebrarum. 

2.  Tensor  tarsi  (Horner's  muscle). 

3.  Corrugator  supercilii. 

The  upper  eyelid  has  a  special  elevator,  termed  the  levator 
palpebrce  superior  is,  but  this  muscle  is  contained  within  the 
orbital  cavity,  and  does  not  come  under  the  notice  of  the 
dissector  at  the  present  stage.  The  examination  of  the  tensor 
tarsi  must  also  be  deferred  until  the  eyelids  are  dissected. 

Internal  Tarsal  Ligament. — If  the  eyelids  be  drawn  out- 
wards, a  prominent  cord-like  ligament  becomes  apparent  on 
the  inner  side  of  the  inner  canthus.  This  extends  outwards 
from  the  nasal  process  of  the  superior  maxillary  bone  to  reach 
the  eyelids,  and  is  termed  the  internal  tarsal  ligament.  It  will 
be  afterwards  more  fully  examined,  but  it  is  necessary  to 
notice  it  at  present,  seeing  that  it  is  closely  connected  with 
the  origin  of  the  orbicularis  palpebrarum. 

Orbicularis  Palpebrarum  (orbicularis  oculi). — This  k-  the 
sphincter  muscle  of  the  palpebral  fissure.  It  is  a  thin  sheet 
of  muscular  fibres,  which  occupies  a  very  considerable  area  of 
the  face.  It  is  customary  to  regard  it  as  being  composed  of 
two  parts,  a  palpebral  and  an  orbital.     The  palpebral  portion 


DISSECTION  OF  THE  FACE  253 

is  the  part  which  lies  upon  the  eyelids.  It  is  thin  and  pale, 
and  its  fibres  arise  from  the  margins  of  the  internal  tarsal 
ligament.  From  these  they  sweep  outwards  upon  the  two 
lids,  describing  a  series  of  gentle  curves,  and  at  the  outer 
canthus  they  obtain  attachment  to  the  external  tarsal  ligament. 
They  form  a  continuous  layer  of  uniform  thickness  in  both 
eyelids,  except  at  their  free  margins.  Here,  close  to  the 
bases  of  the  eyelashes,  there  is  a  more  pronounced  fasciculus, 
which  is  termed  the  ciliary  bundle. 

The  orbital  portion  is  placed  upon  the  margin  of  the 
orbital  opening;  but  it  is  not  confined  to  this.  It  extends 
for  some  distance  beyond  it,  upwards  on  the  forehead,  down- 
wards on  the  cheek,  and  outwards  so  as  to  encroach  upon 
the  temporal  region.  The  fasciculi  which  compose  this  part 
of  the  muscle  are  of  a  darker  and  coarser  type.  They  all 
arise  internally  and  sweep  outwards  around  the  orbital  margin 
in  the  form  of  a  series  of  concentric  loops.  They  take  origin 
(1)  from  the  inner  part  of  the  internal  tarsal  ligament,  (2) 
from  the  internal  angular  process  of  the  frontal  bone,  and 
from  the  ascending  process  of  the  superior  maxillary  bone 
immediately  in  front  of  the  lachrymal  groove. 

Above  and  to  the  inner  side,  the  fasciculi  of  the  orbicularis 
muscle  are  closely  connected,  and  to  a  certain  extent  interlaced 
with  the  fasciculi  of  the  frontal  part  of  the  occipito-frontalis, 
the  corrugator  supercilii  and  the  pyramidalis  nasi,  whilst  from 
its  lower  margin  a  few  delicate  fleshy  bands  are  carried  down- 
wards through  the  soft  fat  to  gain  insertion  into  the  skin  of 
the  cheek. 

Corrugator  Supercilii. — This  is  a  small  but  very  distinct 
band  of  dark-coloured  muscular  fibres  which  can  be  exposed 
by  raising  the  upper  and  inner  part  of  the  orbicularis,  with 
the  frontalis  muscle  which  is  connected  with  it,  from  the 
superciliary  ridge.  The  corrugator  supercilii  will  then  be  seen 
arising  from  the  inner  extremity  of  this  ridge.  Its  fibres  pass 
upwards  and  outwards,  and  the  greater  proportion  of  them 
pass  through  the  fasciculi  of  the  orbicularis  and  frontal 
belly  of  the  occipito-frontalis  to  gain  a  direct  insertion  into 
the  skin  of  the  eyebrow;  one  of  its  muscular  bundles, 
however,  joins  the  orbicularis,  whilst  a  few  others  blend  with 
the  frontalis. 

Oral  Group  of  Muscles. — The  muscles  of  the  lips  and 
mouth  which  are  included  in  this  group  are  the  following : — 


254  HEAD  AND  NECK 


I. 

Orbicularis  oris. 

5- 

Levator  labii  superioris. 

2. 

v             ..       f  major. 
Zygomaticus-!      ■J 
Jb                 y  minor. 

6. 

7- 

Levator  anguli  oris. 
Depressor  anguli  oris. 

3- 

Risorius. 

8. 

Depressor  labii  inferioris 

4- 

Levator    labii    superioris 

9- 

Levator  menti. 

alceque  nasi. 

IO. 

Buccinator. 

Orbicularis  Oris. — The  orbicularis  oris  is  a  sphincter 
muscle  which  surrounds  the  oral  aperture.  The  other 
muscles  of  this  group,  with  the  exception  of  the  levator 
menti,  converge  towards  it.  From  the  nasal  process  of  the 
superior  maxilla,  and  from  the  lower  margin  of  the  orbital 
opening,  the  labial  slip  of  the  levator  labii  superioris  alseque 
nasi,  and  the  levator  labii  superioris  descend  into  the  upper 
lip.  Converging  upon  the  angle  of  the  mouth,  the  dissector 
will  have  little  difficulty  in  recognising  the  zygomaticus 
major,  the  risorius,  and  the  depressor  anguli  oris ;  whilst 
placed  upon  a  deeper  plane  and  extending  towards  the 
same  point  are  the  levator  anguli  oris  and  the  buccinator. 
Entering  the  lower  lip  from  below  is  the  depressor  labii 
inferioris.  The  play  of  the  lips  is  produced  by  the  action  of 
these  muscles  antagonised  to  a  certain  extent  by  the  orbicu- 
laris. The  levator  menti  has  little  connexion  with  the  lips. 
It  only  acts  indirectly  on  the  lower  lip,  as  will  be  seen  when 
its  attachments  are  studied. 

Dissection. — It  is  in  dissecting  these  muscles  that  the  chief  difficulty  will 
be  encountered  in  preserving  the  various  nerves  of  the  face.  Several  large 
branches  of  the  facial  nerve  will  be  found  passing  forwards  under  cover  of 
the  zygomatic  muscles  to  reach  the  under  surface  of  the  levator  labii 
superioris,  where  they  form  a  complicated  plexus  with  the  infra-orbital  nerve. 
Other  branches  proceed  forwards  upon  the  buccinator  muscle,  and  enter 
into  communication  in  front  of  the  masseter  with  the  long  buccal  nerve. 
The  mandibular  division  of  the  facial  nerve  will  also  be  noticed  on  the 
surface  of  the  lower  jaw.  Its  branches  disappear  under  cover  of  the 
depressor  anguli  oris.  All  these  nerves  must  be  carefully  followed  out  as 
the  muscles  are  being  exposed  and  cleaned. 

Zygomaticus  Major,  Risorius,  and  Depressor  Anguli  Oris. 

— These  three  muscles  may  be  grouped  together,  seeing  that 
they  lie  in  the  same  plane  and  run  towards  the  angle  of  the 
mouth.  The  platysma  also  occupies  the  same  plane,  and 
many  of  its  fibres  blend  with  the  depressor  anguli  oris,  whilst 
others  are  carried  forwards  into  the  risorius. 

The  zygomaticus  major  is  a  long  fleshy  band  which  springs 
from  the  malar  bone  immediately  in  front  of  the  zygomatic 
suture.      From  this  it  proceeds  downwards  and  forwards,  and 


DISSECTION  OF  THE  FACE 


255 


at  the  angle  of  the  mouth  some  of  its  fibres  are  inserted  into 
the  skin,  whilst  others  blend  with  the  orbicularis  oris  and  with 
the  depressor  anguli  oris. 

The    risorius    is    sometimes    regarded    as    a   continuation 


Frontalis 


Orbicularis  palpebrarum 


Levator  labii  superioris, 
aljeque  na 

Compressor  naris 

Levator  labii  superioris 

Zygomaticus  major 

Levator  anguli  oris 

Risorius 


PyramidalU 


-Orbicularis  oris 


Orbicularis  oris 


Depressor  labii  inferioris 
Depressor  anguli  oris 


Fig.  97. — The  Facial  Muscles. 

forwards  on  the  face  of  the  posterior  fibres  of  the  platysma ; 
more  frequently  it  takes  independent  origin  from  the  fascia 
covering  the  masseter,  although  some  of  its  fibres  come 
directly  from  the  platysma.  It  is  composed  of  a  few  slender 
fasciculi  which   pass  transversely   forwards  in   the  fatty  tissue 


256  HEAD  AND  NECK 

of  the   cheek    to   the   angle   of  the   mouth,   where  they  are 
inserted  into  the  skin. 

The  depressor  anguli  oris  is  a  flat  triangular  muscle 
which  presents  a  broad  origin  from  the  external  oblique 
line  of  the  lower  jaw.  From  this  it  proceeds  upwards  to 
the  angle  of  the  mouth.  Here  its  fibres,  which  are  collected 
in  the  form  of  a  narrow  bundle,  are  partly  inserted  into  the 
skin,  and  partly  prolonged  into  the  upper  Up  in  the  orbi- 
cularis oris. 

The  mental  branch  of  the  mandibular  nerve  and  its  ac- 
companying artery  appear  on  the  face  under  cover  of  this 
muscle. 

Levator  Labii  Superioris  Alaeque  Nasi. — This  is  a  thin 
fleshy  band  which  lies  along  the  side  of  the  nose.  It  is 
narrow  above  where  it  arises  from  the  nasal  process  of  the 
superior  maxillary  bone,  but  it  expands  somewhat  as  it 
proceeds  downwards,  and  finally  divides  into  two  slips — 
a  nasal  and  a  labial.  The  inner  and  smaller  nasal  slip  is 
inserted  into  the  wing  of  the  nose,  whilst  the  labial  slip  is 
prolonged  into  the  upper  lip,  where  some  of  its  fibres  blend 
with  the  orbicularis  oris,  and  others  obtain  a  direct  attach- 
ment to  the  skin. 

Levator  Labii  Superioris. — This  band-like  muscle  arises 
from  the  lower  margin  of  the  orbital  opening,  immediately 
above  the  infra-orbital  foramen.  It  takes  the  form  of  a  flat 
band  which  proceeds  downwards  and  slightly  inwards,  to  end 
in  the  skin  of  the  upper  lip.  Under  cover  of  this  muscle 
the  large  iftfra-orbital  nerve  emerges  on  the  face,  and  joins 
with  branches  of  the  facial  nerve  in  the  infra-orbital  plexus. 

Zygomaticus  Minor. — The  zygomaticus  minor  may  be 
looked  upon  as  a  part  of  the  preceding  muscle.  It  is  also 
closely  connected  with  the  orbicularis  palpebrarum,  from 
which  some  of  its  fasciculi  are  often  derived,  and  it  lies  on 
the  same  plane  as  those  slender  slips  which  the  orbicularis 
oris  sends  downwards  from  its  lower  margin  to  the  skin  of  the 
cheek. 

It  is  a  slender  fleshy  bundle  which  arises  from  the  malar 
bone  in  front  of  the  zygomaticus  major,  and  passes  down- 
wards and  forwards  to  join  the  outer  margin  of  the  levator 
labii  superioris. 

Levator  Anguli  Oris  (musculus  caninus). — The  origin  of 
this  muscle   is   hidden    by  the    levator   labii    superioris.      It 


DISSECTION  OF  THE  FACE  257 

springs  from  the  upper  part  of  the  canine  fossa,  immediately 
below  the  infra-orbital  foramen,  and  proceeds  downwards 
and  outwards  to  the  angle  of  the  mouth.  Here  some  of 
its  fasciculi  mingle  with  those  of  the  orbicularis  and  enter 
the  lower  lip,  whilst  others  gain  a  direct  insertion  into  the 
skin. 

It  should  be  noticed  that  the  bundle  of  fibres  which  is 
given  by  the  depressor  anguli  oris  to  the  upper  lip,  and  the 
bundle  which  is  contributed  by  the  levator  anguli  oris  to 
the  lower  lip,  decussate  with  each  other  at  the  angle  of  the 
mouth  (Fig.  99). 

Depressor  Labii  Inferioris  (quadratus  labii  inferioris). — 
The  depressor  labii  inferioris  is  a  quadrate  muscle  partially 
hidden     by    the    depressor    anguli    oris,     which    overlaps    it 


Fig.  98. — Arrangement  of  the  Fibres  of  the  Buccinator  Muscle 
at  the  Angles  of  the  Mouth. 

(Fig.  97).  It  springs  from  the  lower  jaw  by  a  linear  origin 
which  extends  from  the  symphysis  to  a  point  a  short  distance 
beyond  the  mental  foramen,  and  passing  upwards,  with  an 
inclination  inwards,  it  joins  the  corresponding  muscle  of 
the  opposite  side,  and  is  inserted  into  the  skin  of  the  lower 
lip.  Amongst  the  fleshy  fasciculi  which  compose  this  muscle 
there  is  a  large  admixture  of  fat,  which  renders  it  rather  pale 
in  colour. 

Dissection.  —  The  buccinator  muscle  must  be  cleaned  with  care, 
because  branches  from  the  facial  nerve  and  the  long  buccal  nerve  form 
a  plexus  upon  its  surface,  and  great  numbers  of  nerves  enter  it,  both  for 
the  purpose  of  supplying  it,  and  also  for  the  purpose  of  reaching  the 
mucous  membrane  of  the  mouth  which  lines  its  deep  surface. 

Buccinator  Muscle. — This  important  muscle  occupies  the 
interval  between  the  upper  and  lower  jaws,  and  forms  the 
chief  muscular  layer  of  the  cheek.  Above  and  below,  its 
fibres   take   origin    from   the   outer    surface    of   the    alveolar 

vol.  11 — 17 


258 


HEAD  AND  NECK 


margins  of  both  of  these  bones  as  far  forwards  as  the  first 
molar  tooth.  Behind,  its  posterior  border  is  attached  to  the 
pterygo-maxillary  ligament,  which  acts  as  the  bond  of  union 
between  it  and  the  superior  constrictor  muscle  of  the 
pharynx.  This  attachment  cannot  be  studied  at  present, 
but  will  be  afterwards  examined  in  the  dissection  of  the 
pharyngeal  wall.  Anteriorly,  it  abuts  against  the  angle  of 
the  mouth,  and  its  fibres  blend  with  the  orbicularis  oris,  a 
large    part    of  which    it    forms.      But   the    manner   in   which 


Levator  labii  superioris  alaeque  nasi 


Levator  labii  superioris 


Levator  anguli  oris 


Depressor  anguli  oris 


Depressor  labii  inferioris 


Fig.  99. — Diagram  of  the  Orbicularis  Oris  Muscle.     The  fibres  which 
enter  it  from  the  buccinator  are  not  represented. 


the  fibres  of  this  muscle  enter  the  orbicularis  must  be 
examined.  The  upper  and  lower  fibres  pass  directly  into 
the  corresponding  lip ;  the  middle  fibres,  on  the  other 
hand,  decussate  at  the  angle  of  the  mouth,  so  that  the 
lower  fibres  of  this  series  enter  the  upper  lip,  whilst  the 
higher  fasciculi  reach  the  lower  lip  (Fig.  98). 

Orbicularis  Oris. — The  orbicularis  oris  is  composed  of 
fleshy  fasciculi  which  sweep  round  the  oral  aperture  in  the 
interval  between  the  skin  and  mucous  membrane,  and  form 
a  considerable  part  of  the  substance  of  the  two  lips.  Its 
upper  margin  extends  upwards  as  high  as  the  nose,   whilst 


DISSECTION  OF  THE  FACE  259 

its   lower   margin    corresponds    to    the    groove    on    the    face 
which  intervenes  between  the  chin  and  the  lower  lip. 

The  fibres  which  compose  the  orbicularis  oris  are  derived 
from  many  different  sources.  The  chief  bulk  of  the  muscle 
is  formed  by  the  continuation  into  the  lips  of  fibres  which 
belong  to  the  buccinator,  the  levator  anguli  oris,  and  the 
depressor  anguli  oris  of  each  side. 

The  fasciculi  of  the  buccinator  muscle  arrange  themselves  at  the  angle 
of  the  mouth,  in  the  manner  already  described,  into  two  bundles,  and 
these  are  prolonged  onwards  into  the  two  lips  so  as  to  encircle  the  oral 
aperture,  and  become  continuous  with  the  corresponding  fasciculi  of  the 
opposite  side.  These  fibres  form  the  marginal  part  of  the  orbicularis,  and 
also  the  deeper  peripheral  part.  The  labial  portions  of  the  levator  anguli 
oris  and  the  depressor  anguli  oris  are  arranged  quite  differently.  The 
labial  slip  from  the  levator  anguli  oris  passes  into  the  lower  lip,  and  the 
corresponding  slip  from  the  depressor  anguli  oris  is  continued  into  the 
upper  lip.  In  neither  case  do  the  fibres  reach  the  opposite  angle  of  the 
mouth  ;  they  are  inserted  into  the  skin  at  the  middle  of  each  lip.  The 
fibres  which  come  from  these  sources  form  the  superficial  peripheral  part 
of  the  orbicularis. 

In  addition  to  the  fibres  derived  from  these  three  muscles, 
the^orbicularis  oris  receives  certain  slips  which  present  special 
attachments.  Two  are  provided  for  each  side  of  the  upper 
lip,  viz.,  (1)  the  naso-labial  band  (m.  naso-labialis),  and  (2)  the 
superior  incisive  band  (m.  incisivus  superior) ;  and  one,  the 
inferior  incisive  band  (m.  incisivus  inferior),  is  given  to  each 
side  of  the  lower  lip.  The  naso-labial  band  is  a  rounded 
bundle  which  arises  from  the  lower  border  of  the  nasal  septum, 
and  turns  outwards  into  the  orbicularis  oris.  The  superior 
incisive  bundle  takes  origin  from  the  incisor  fossa  of  the  superior 
maxilla,  and  turns  outwards  in  the  orbicularis ;  whilst  the 
inferior  incisive  bundle  arises  from  the  corresponding  fossa  of 
the  mandible,  and  presents  similar  connexions  in  the  lower 
lip. 

The  incisive  slips  can  be  easily  exposed  by  everting  the  lips,  and  re- 
moving the  mucous  membrane  from  the  neighbourhood  of  these  fossae.  By 
this  dissection  two  other  small  muscles  will  be  displayed  :  (1)  the  depressor 
ake  nasi  to  the  inner  side  of  the  superior  incisive  slip  ;  and  (2)  the  levator 
menti  to  the  inner  side  of  the  inferior  incisive  slip.  The  concentric  arrange- 
ment of  the  fibres  of  the  orbicularis  oris  is  well  seen  when  the  mucous 
membrane  is  removed  from  the  deep  surface  of  the  lips.  Numerous  labial 
glands  which  lie  between  the  muscle  and  the  mucous  membrane  are  dis- 
played by  the  same  proceeding. 

Levator  Menti. — To  expose  this  small  muscle  the  lower 
lip  must  be  everted,  and  the   mucous   membrane   removed   at 


26o  HEAD  AND  NECK 

the  side  of  the  frenum  of  the  lower  lip.  It  is  a  short,  well- 
marked  fleshy  band,  which  springs  from  the  incisor  fossa  of 
the  lower  jaw,  and  proceeds  downwards  and  slightly  forward, 
to  be  inserted  into  the  skin  of  the  chin  between  the  two 
depressor  muscles  of  the  lower  lip. 

Nasal    Group    of   Muscles.  —  Under    this   head   are   com- 
prised : — 


1.  Compressor  naris. 

2.  Levator  labii  superioris 

akeque  nasi   (already 


3.  Pyramidalis  nasi. 

4.  Depressor  alae  nasi. 

5.  Dilatator  naris  posterior. 


examined).  6.   Dilatator  naris  anterior. 

Compressor  Naris. — -This  is  a  flat  triangular  muscle  which 
springs  by  a  pointed  fleshy  origin  from  the  superior  maxillary 
bone  close  to  the  margin  of  the  anterior  nasal  aperture  and 
under  cover  of  the  levator  labii  superioris  alaeque  nasi.  From 
this  it  extends  inwards  and  upwards,  and  expands  into  an 
aponeurosis,  which  covers  the  cartilaginous  part  of  the  nose, 
and  in  the  mesial  plane  becomes  continuous  with  the  corre- 
sponding aponeurosis  of  the  opposite  side. 

Pyramidalis  Nasi. — This  narrow  slip  of  muscular  fibres 
springs  from  the  aponeurosis  of  the  compressor  naris,  and 
passes  upwards  upon  the  nasal  bone.  Some  of  the  fibres 
gain  a  direct  insertion  into  the  skin  over  the  lower  part  of 
the  forehead ;  others  are  continuous  with  the  fasciculi  of  the 
frontalis  muscle. 

Depressor  Alse  Nasi. — This  is  a  minute  muscle,  the  origin  of  which  has 
already  been  displayed  by  the  removal  of  the  mucous  membrane  at  the  side 
of  the  frenum  of  the  upper  lip.  It  springs  from  the  incisor  fossa  of  the 
superior  maxilla  above  and  to  the  inner  side  of  the  superior  incisive  slip  of 
the  orbicularis  oris  muscle.  Its  outer  margin  is  usually  more  or  less 
blended  with  the  compressor  naris,  and  its  fibres  arch  upwards  and  forwards 
to  become  attached  to  the  lower  and  back  part  of  both  the  ala  and  the 
septum  of  the  nose. 

Dilatator  Muscles. — These  can  rarely  be  satisfactorily  displayed.  The 
fibres  which  compose  them  are  pale  and  feeble,  and  they  are  embedded  in 
the  dense  tissue  at  the  lower  and  outer  part  of  the  nose  immediately  above 
the  aperture.  An  anterior  slip  (levator  proprius  alse  nasi  anterior)  is  placed 
on  the  lower  part  of  the  side  of  the  nose  towards  the  fore-part  of  the  nostril, 
and  a  posterior  slip  (levator  proprius  alee  nasi  posterior)  at  a  short  distance 
behind  this. 

Nerves  of  the  Face. — The  nerves  in  this  region  may  be 
divided  into  two  sets  according  as  they  supply  the  skin  or 
the  muscles  of  the  face.  The  motor  nerve  is  the  nervus 
facialis.     The  sensory  nerves  come  from  various  sources,  and 


DISSECTION   OF  THE   FACE  261 

they  reach  the  face  either  directly  or  indirectly  through   the 
medium  of  filaments  which  join  branches  of  the  facial  nerve. 
The  following  table  shows  the  derivation  of  these  nerves : — 


Nerves  of  the  Face. 
Facial  nerve. 


I.  Motor. 

II.  Sensory. 

(a)  Appearing  directly  on  the  face. 

1.  Facial  branches  of  the  great  auricular  nerve. 

2.  Branches  of  the  trigeminal  nerve  (5th  cranial),  viz.  : — 

f  Supra-orbital. 
x?         n.        i4.    1     •        Supra-trochlear. 
°mdWision         miC   !  Infra-trochlear. 

Palpebral  branch  of  the  lachrymal. 
\  Nasal. 

t,  ,,  (  Infra-orbital, 

from     the    superior      c   ,      .  , 

.„         j-   •  •        -[  Subcutaneus  malae. 
maxillary  division.       ~  ,  ,  ,     r .,         ...  , 

3  I  Temporal  branch  of  the  orbital. 

^  .         •   c    •       i  Auriculo-temporal. 

rrom      the      inferior      T  ,  ,  r 

...  ,.   .  .        -    Lone  buccal, 

maxillary  division.    I  Mei£al> 

{b)  Reaching  the  face  indirectly. 

1.  Communicating   branches  from    the   great    auricular    nerve   to  the 

facial  nerve. 

2.  Communicating  branches  from   the  auriculo-temporal  nerve  to  the 

facial  nerve. 

Whilst,  therefore,  the  motor  filaments  come  from  one 
source  alone,  the  sensory  nerves  are  derived  partly  from  the 
cervical  plexus  through  the  great  auricular  nerve,  but  chiefly 
from  the  trigeminal  nerve,  each  division  of  which  furnishes 
several  branches  to  the  face. 

Dissection. — The  facial  nerve  is  already,  in  a  great  measure,  displayed. 
Its  exit  from  the  stylo-mastoid  foramen  can  be  rendered  more  evident  by 
chipping  off  the  free  projecting  part  of  the  mastoid  process.  In  doing  this, 
first  use  the  saw,  and  then  complete  the  severance  with  the  chisel.  Care 
must  be  taken  not  to  injure  the  posterior  auricular  branch  of  the  facial 
nerve.  By  this  proceeding  a  good  view  can  be  obtained  of  the  origin  of 
the  posterior  belly  of  the  digastric,  of  the  stylo-mastoid  branch  of  the 
posterior  auricular  artery  as  it  enters  the  foramen  of  the  same  name  upon 
the  facial  nerve,  and  also  of  the  occipital  artery  in  the  deepest  part  of  its 
course. 

Facial  Nerve  (nervus  facialis). — The  trunk  of  the  facial 
nerve  emerges  from  the  stylo-mastoid  foramen  and  proceeds 
forwards  in  the  substance  of  the  parotid  gland.  Near  the 
posterior  margin  of  the  ascending  ramus  of  the  lower  jaw,  it 
ends  by  dividing  into  two  branches,  termed  respectively  the 
temporo-farial  and  the  cervicofacial  divisio?is.  From  this  part 
11     17" 


262 


HEAD  AND  NECK 


s. 


of  the  nerve  three  branches  arise,  viz. : — the  posterior  auricular 
nerve,  the  nerve  to  the  posterior  belly  of  the  digastric  muscle, 
and  the  nerve  to  the  stylo-hyoid  muscle. 

The  posterior  auricular  nerve  has  already  been  followed  out 
in  its  distribution  to  the  retrahens  auriculam,  attollens 
auriculam,  and  posterior  belly  of  the  occipito-frontalis  (p. 
no).      Its  origin  is  now  exposed,  and  it  will  be  seen  to  arise 


Supra-orbital 


Temporal  branch 
of  orbital 


Supra-trochlear 
Lachrymal 


Infra-trochlear 


Mental 


Malar  branch 
of  orbital 


Auriculo- temporal 


Posterior  auricular 

Trunk  of  facial 

Branch  to  posterior 

belly  of  digastric 

and  stylo-hyoid 


Long  buccal 


Fig.  100. — Nerves  of  the  Face.      The  facial  nerve  is  depicted  in  yellow, 
the  sensory  branches  of  the  trigeminal  in  black. 

1,  2,  3.  The  three  branches  of  the  temporo-facial  division  of  the  facial  nerve. 
4,  5,  6.  The  three  branches  of  the  cervico-facial  division  of  the  facial  nerve. 

from  the  facial  trunk  immediately  after  this  issues  from  the 
stylo-mastoid  foramen. 

At  this  stage  it  may  be  possible  to  make  out  a  communication  between 
the  auricular  branch  of  the  pneumogastric  (Arnold's  nerve)  and  the 
posterior  auricular  branch  of  the  facial.  Arnold's  nerve  emerges  from  the 
interval  between  the  mastoid  process  and  the  auditory  meatus  ;  and  after 
sending  a  branch  to  join  the  posterior  auricular  nerve,  it  ends  in  filaments 
for  the  integument  on  the  posterior  aspect  of  the  ear. 

The   nerve    to    the  posterior   belly    of  the    digastric   (ramus 
digastricus)  is  a  stout,  short  branch  which  inclines  downwards 


DISSECTION  OF  THE   FACE  263 

and  forwards  and  soon  divides  into  several  filaments  which 
enter  the  upper  surface  of  this  muscle.  One  of  these  twigs 
usually  passes  through  the  muscle  to  effect  a  communication 
with  the  glosso-pharyngeal. 

The  nerve  to  the  stylo-hyoid  (ramus  stylohyoideus)  is  a 
longer  and  more  slender  filament,  which  generally  arises  in 
common  with  the  preceding,  and  sinks  into  the  posterior 
aspect  of  this  muscle. 

Temporo-facial  Division. — The  temporo-facial  division  of 
the  facial  nerve  is  prolonged  forwards  through  the  parotid 
gland,  and  at  once  divides  into  numerous  branches  which 
radiate  widely  from  each  other,  and  stretch  over  an  area 
extending  from  the  ear  behind  to  the  margin  of  the  upper  lip 
below.  Whilst  within  the  substance  of  the  parotid  gland,  the 
temporo-facial  nerve  crosses  the  external  carotid  artery  near 
its  termination,  and  also  the  temporo-maxillary  vein.  It 
receives  two,  or  it  may  be  three,  stout  branches  of  com- 
munication from  the  auriculo-temporal  nerve,  and  forms  a 
plexiform  arrangement  with  the  branches  of  the  cervico-facial 
division  in  the  midst  of  the  parotid  gland.  This  receives  the 
name  of  the  pes  anserifius  or  plexus  parotideus. 

The  branches  into  which  this  portion  of  the  facial  trunk 
divides  are  classified,  according  to  the  direction  which  they 
take,  into— 

1.  Temporal. 

2.  Malar. 

3.  Infra-orbital. 

The  temporal  branches,  three  or  four  in  number,  emerge 
from  the  upper  border  of  the  parotid,  and  are  carried  up- 
wards over  the  zygomatic  arch  to  the  temporal  region. 
Here  they  supply  the  attrahens  auriculam,  the  frontal  belly 
of  the  occipito-frontalis,  the  orbicularis  palpebrarum,  and 
the  corrugator  supercilii.  They  communicate  with  several 
branches  of  the  trigeminal  or  fifth  cranial  nerve,  more 
especially  with  the  auriculo-temporal,  the  temporal  branch  of 
the  orbital,  and  the  supra-orbital. 

The  malar  bra?iches  are  small,  run  forwards  upon  the  malar 
bone,  and  end  in  filaments,  which  enter  the  outer  and  lower 
part  of  the  orbicularis  palpebrarum  muscle.  Some  of  the 
twigs  may  be  traced  to  the  upper  and  lower  eyelids.  On  the 
malar  bone  they  communicate  with  the  malar  branch  of  the 
Orbital  nerve,  and  in  the  eyelids  they  are  connected  with  the 
n—176 


264  HEAD  AND  NECK 

various  branches  of  the  trigeminal  nerve  which  are  distributed 
to  these  structures. 

The  infra-orbital  branches  are  larger  than  either  of  the 
preceding,  and  they  run  horizontally  forwards  along  the 
lower  border  of  the  malar  bone,  and  under  cover  of  the 
zygomaticus  major  to  the  infra-orbital  region.  Here  they 
supply  twigs  to  the  muscles  in  this  neighbourhood  as  well  as 
to  the  muscles  of  the  nose.  They  likewise  communicate 
with  the  infra- orbital,  nasal,  and  infra -trochlear  nerves. 
With  the  infra-orbital  nerve  they  form  a  complicated  plexus 
(the  infra-orbital  plexus),  under  cover  of  the  levator  labii 
superioris. 

Cervicofacial  Division. — The  cervico-facial  division  of  the 
facial  trunk  is  smaller  than  the  temporo-facial  division.  It 
proceeds  forwards,  with  a  slight  inclination  downwards,  and 
breaks  up  in  the  substance  of  the  parotid  into  three  main 
branches,  which  are  termed  from  the  course  which  they  take — 

i.   Buccal. 

2.  Mandibular. 

3.  Cervical. 

In  the  parotid  gland  the  cervico-facial  division  crosses  the 
external  carotid  artery  and  receives  several  communicating 
twigs  from  the  great  auricular  nerve. 

The  buccal  branches  run  forwards  upon  the  buccinator 
muscle  to  the  angle  of  the  mouth,  where  they  end  in  fila- 
ments for  the  orbicularis  oris.  They  supply  the  buccinator 
muscle,  and  form,  with  the  long  buccal  branch  of  the  inferior 
maxillary  division  of  the  fifth  nerve,  a  plexus  around  the 
facial  vein. 

The  mandibular  branch  proceeds  forwards  upon  the  lower 
jaw  to  reach  the  muscles  in  connexion  with  the  lower  lip. 
Under  cover  of  the  depressor  anguli  oris  it  communicates 
with  the  mental  branch  of  the  inferior  dental  nerve. 

The  cervical  or  infra-mandibular  branch  has  already  been 
examined  in  the  dissection  of  the  neck  (p.  182). 

Sensory  Branches  to  the  Face  from  the  Trigeminal  Nerve. 
— The  branches  which  come  from  the  ophthalmic  division  of 
the  trigeminal  nerve  may  first  be  studied.  Of  these,  two  go 
to  the  skin  of  the  forehead  and  scalp — viz.,  the  supra-orbital 
and  the  supra-trochlear ;  two  to  the  eyelids — viz.,  the  palpebral 
branch  of  the  lachrymal  and  the  infra-trochlear ;  and  one,  the 
nasal,  to  the  skin  of  the  nose. 


DISSECTION  OF  THE  FACE  265 

The  supra- orbital  and  the  supra-trochlear  have  already  been 
dissected  in  the  scalp  (pp.  107,  109).  They  should  now  be 
followed  downwards  to  the  point  where  they  turn  round  the 
orbital  arch  of  the  frontal  bone.  This  can  be  done  by 
cutting  through  the  frontal  belly  of  the  occipito-frontalis  and 
the  orbicularis  palpebrarum,  under  cover  of  which  they  pass 
upwards.  The  supra-orbital  quits  the  orbit  by  the  supra- 
orbital notch  or  foramen,  and  the  supra-trochlear  at  a  point 
internal  to  this.  Both  nerves  give  twigs  downwards  to  the 
skin  and  conjunctiva  of  the  upper  eyelid. 

The  palpebral  or  terminal  branch  of  the  lachrymal  appears 
in  the  upper  eyelid  above  the  outer  canthus,  where  it  pierces 
the  superior  palpebral  ligament,  and  gives  filaments  to  the 
skin  and  conjunctiva. 

The  infra-trochlear  nerve  will  be  found  above  the  internal 
tarsal  ligament  and  the  inner  canthus.  The  twigs  into  which 
it  divides  communicate  with  the  facial  and  supply  the  lachrymal 
sac,  the  conjunctiva  and  the  skin  of  the  eyelids,  and  the  root 
of  the  nose. 

The  nasal  nerve  (ramus  nasalis  externus)  reaches  the  face 
on  the  side  of  the  movable  part  of  the  nose.  To  expose  it, 
divide  the  compressor  naris,  and  it  will  be  found  appearing 
between  the  lower  margin  of  the  nasal  bone  and  the  upper 
lateral  cartilage.  It  gives  branches  to  the  integument  of  the 
nose  and  communicates  with  the  facial  nerve.  It  can  be 
traced  downwards  under  cover  of  the  compressor  muscle  to 
the  tip  of  the  nose. 

The  branches  of  the  superior  maxillary  division  of  the 
trigeminal  nerve  which  appear  on  the  face  are  three  in 
number— viz.,  the  temporal  branch  of  the  orbital  nerve,  which 
has  been  already  studied  (p.  109);  the  malar  branch  of  the 
orbital  nerve  ;  and  the  infra-orbital. 

The  malar  nerve  (ramus  zygomatico-facialis)  is  an  exceedingly 
minute  twig  which  emerges  on  the  face  through  a  minute 
foramen  on  the  outer  surface  of  the  malar  bone,  a  short 
distance  behind  the  external  margin  of  the  orbit.  To  expose 
it  the  orbicularis  palpebrarum  must  be  carefully  raised  from 
the  bone  in  an  upward  direction. 

The  infra-orbital  nerve  (nervus  infra-orbitalis)  is  the  terminal 
part  of  the  superior  maxillary  division  of  the  trigeminal  nerve. 
It  is  a  large  branch  which  issues  from  the  infra-orbital  foramen 
under  cover  of  the  levator  labii  superioris.     It  forms,  with  the 


266  HEAD   AND   NECK 

facial  nerve,  a  plexus,  and  distributes  palpebral,  nasal,  and 
labial  branches.  The  palpebral  twigs  turn  upwards  to  supply 
the  skin  and  conjunctiva  of  the  lower  eyelid ;  the  nasal 
bra?iches  incline  inwards  upon  the  side  of  the  nose ;  and  the 
labial  branches  run  downwards  to  end  in  the  skin  and  mucous 
membrane  of  the  upper  lip. 

From  the  inferior  maxillary  division  of  the  trigeminal  three 
nerves  are  furnished  to  the  face — viz.,  the  auriculotemporal, 
which  has  been  described  on  p.  no;  the  long  buccal  nerve ; 
and  the  mental  nerve. 

The  long  buccal  nerve  (n.  buccinatorius)  will  be  found 
coming  out  from  under  cover  of  the  anterior  border  of  the 
masseter  muscle.  Its  branches  communicate  freely  with  the 
facial  nerve  around  the  facial  vein,  and  supply  the  skin  and 
the  mucous  membrane  of  the  cheek.  Those  which  go  to  the 
mucous  membrane  pierce  the  buccinator  muscle. 

The  mental  nerve  (nervus  mentalis)  is  a  large  branch  of  the 
mandibular  or  inferior  dental  nerve  which  appears  through  the 
mental  foramen  of  the  lower  jaw  under  cover  of  the  depressor 
anguli  oris.  It  communicates  with  the  facial,  and  supplies  the 
mucous  membrane  of  the  lower  lip,  and  the  integument  of 
the  chin  and  lower  lip.  The  mental  foramen  through  which 
the  nerve  emerges  lies  directly  below  the  interval  between  the 
two  bicuspid  teeth. 

If  a  line  be  drawn  from  the  supra-orbital  notch  to  the  interval  between 
the  two  lower  bicuspid  teeth,  and  from  that  onwards  to  the  base  of  the 
lower  jaw,  it  will  pass  over  or  close  to  the  infra -orbital  and  mental 
foramina.  This  line  therefore  can  be  used  as  a  guide  in  searching  for 
these  nerves. 

Arteries  of  the  Face. — There  are  two  main  channels 
concerned  in  conveying  blood  to  the  face — viz.,  (i)  the 
transverse  facial  artery,  a  branch  of  the  superficial  temporal, 
already  examined  (p.  251) ;  (2)  the  facial  artery,  a  branch  of 
the  external  carotid.  In  addition  to  these  a  great  number  of 
smaller  vessels  appear  on  the  face  with  the  sensory  branches 
of  the  trigeminal  nerve.  Those  which  accompany  the 
branches  of  the  ophthalmic  division  are  derived  from  the 
ophthalmic  artery,  whilst  those  associated  with  the  branches 
of  the  superior  and  inferior  maxillary  divisions  proceed  from 
the  internal  maxillary  artery. 

Facial  Artery  (arteria  maxillaris  externa).  —  The  facial 
artery  is  not  infrequently  small  in   size.      In  such  cases  its 


DISSECTION  OF  THE  FACE 


267 


deficiency  is  compensated  for  by  an  increase  in  the  size  of 
the  transverse  facial,  or  of  some  of  the  other  vessels  which 
appear  on  the  face. 

The  course  of  the  facial  artery  in  the  neck  has  already 


Superficial  temporal 


|\  Frontal  branch  of 

jm^-' ophthalmic  artery 
Ntf     Supra-orbital  branch  of  the 
MSst""  ophthalmic  artery 


ransverse  facial 

Angular 
Lateral  nasal 


fra-orbital 
Superior  coronary 


'^iS^cs*      Inferior  coronary 
Inferior  labial 


Buccal  branch  of  internal  maxillary 

Facial 
FlG.   ioi.  —  Arteries  ol  the  I 

been  noted  (p.  237).  It  enters  the  face  by  passing  on  to  the 
mandible  immediately  in  front  of  the  masseter  muscle.  It 
then  takes  a  very  tortuous  course  forwards  and  upwards  to  a 
point  a  short  distance  behind  the  angle  of  the  mouth  ;  from 
this  it  ascends  to  the  inner  canthus  of  the  eye,  and,  much 
reduced  in  size  by  the  numerous  branches  it  has  given  off,  it 


268  HEAD  AND  NECK 

terminates  by  anastomosing  with  the  nasal  branch  of  the 
ophthalmic  artery.  Throughout  its  whole  length  it  is 
comparatively  superficial.  It  is  true  that  it  is  placed  some- 
what deeply  in  the  fat  of  the  cheek,  but  the  only  muscles 
which  cover  it  are,  from  below  upwards :  the  platysma,  the 
risorius,  the  zygomaticus  major,  and  the  levator  labii  superi- 
oris.  Its  terminal  part  is  usually  embedded  in  the  midst  of 
the  fibres  of  the  levator  labii  superioris  alaeque  nasi.  The 
parts  upon  which  it  rests  as  it  extends  through  the  face  will 
be  seen  to  be — (i)  the  lower  jaw  ;  (2)  the  buccinator ;  (3)  the 
levator  anguli  oris.  The  facial  vein  does  not  accompany  it 
closely  in  the  face,  but,  above  the  level  of  the  lower  jaw,  lies 
at  some  distance  behind  it.  Several  branches  of  the  facial 
nerve  cross  it. 

Branches  of  the  Facial  Artery.  —  The  branches  which 
arise  from  the  facial  artery  are  very  numerous.  Some  of 
inconsiderable  size  pass  backwards.  They  are  distributed  to 
parts  in  the  buccal,  masseteric,  and  malar  regions,  and 
anastomose  with  the  transverse  facial,  the  buccal,  and  the 
infra-orbital  arteries.  Others  proceed  forwards,  and,  being 
of  larger  size,  they  receive  special  designations.  They 
are : — 

1.   Inferior  labial. 


2.   Inferior  coronary. 


3.  Superior  coronary. 

4.  Lateral  nasal. 


5.   Angular. 

The  inferior  labial  arises  immediately  above  the  base  of 
the  lower  jaw,  and  is  carried  forwards  under  cover  of  the 
depressor  anguli  oris  to  supply  the  parts  in  connexion  with 
the  chin  and  lower  lip.  It  anastomoses  with  the  mental,  the 
terminal  branch  of  the  submental,  and  the  inferior  coronary 
arteries. 

The  inferior  coronary  takes  origin  opposite  the  angle  of  the 
mouth,  and  runs  inwards  in  the  lower  lip  near  its  free  margin 
between  the  mucous  membrane  and  the  orbicularis  oris.  In 
a  well-injected  subject  it  will  be  seen  shining  through  the 
mucous  membrane  when  the  lip  is  everted.  It  anastomoses 
with  its  fellow  of  the  opposite  side  and  with  the  inferior 
labial. 

The  superior  coronary  arises  under  cover  of  the  zygomaticus 
major,  and  is  related  to  the  upper  lip  in  the  same  manner 
that  the  inferior  coronary  is  related  to  the  lower  lip.  It  is 
generally  of  larger  size.     It  gives  off  a  branch  called  the  septal 


DISSECTION  OF  THE  FACE 


269 


Crus  antiheliois 

Darwin's 

tubercle 

Fossa  scaphoidia 

Helix  4 


Antitragus 


Fossa  triangularis 
Crus  antihelicis 
Concha 

Crus  helicis 

Tragus 

Incisura 

intertragica 


artery,  which  runs  along  the  lower  border  of  the  nasal  septum 
and  distributes  twigs  as  far  as  the  tip  of  the  nose. 

The  lateral  nasal  artery  is  a  branch  which  is  given  to  the 
side  of  the  nose,  and  as  a  rule  passes  forwards  under  cover  of 
the  levator  labii  superioris  alaeque  nasi. 

The  angular  artery  is  the  name  that  is  applied  to  the 
terminal  part  of  the  facial  artery.  It  anastomoses  with  the 
nasal  branch  of  the  ophthalmic  artery. 

Facial  Vein  (vena  facialis  anterior).  —  The  facial  vein 
begins  at  the  inner  canthus  of  the  eye,  in  a  well-marked 
venous  trunk  called  the  angular  vein,  which  is  formed  by  the 
union  of  the  supraorbital  and  frontal  veins  (p.  111).  The 
course  which  the  facial  vein  takes  is  not  nearly  so  tortuous 
as  that  of  the  corre- 
sponding artery ;  it 
lies  behind  the  artery 
and  is  separated  from 
it  by  a  considerable 
interval.  Below  the 
malar  bone  it  pro- 
ceeds in  a  nearly 
vertical  direction 
along  the  anterior 
border  of  the  mas- 
seter  muscle,  and  at 
the  base  of  the  lower  jaw  the  two  vessels  come  together. 

Numerous  tributaries  join  the  facial  vein  as  it  courses 
through  the  face,  and  a  large  branch  called  the  deep  facial 
connects  it  with  the  pterygoid  plexus  of  veins. 

Auriele  or  Pinna. — Before  dissecting  the  auricle,  it  is  well 
to  learn  the  names  of  its  various  parts,  and  note  the  position 
which  they  hold  in  relation  to  each  other.  The  concha  is  the 
wide  and  deep  fossa  which  leads  into  the  external  meatus ; 
the  anti/ielix  is  the  curved  prominence  which  bounds  this 
posteriorly ;  the  helix  is  the  folded  or  incurved  margin  of  the 
pinna  ;  and  the  lobule  is  its  soft  dependent  part.  The  concha 
is  partially  subdivided  into  an  upper  and  a  lower  part  by  the 
commencement  of  the  helix,  which  curves  upwards  and  for- 
wards on  its  floor  to  become  continuous  with  the  anterior 
border  of  the  pinna.  This  portion  of  the  helix  is  called  the 
crus  helicis.  A  small  prominence  in  front  of  the  meatus,  and 
projecting  backwards  so  as  to  overshadow  it,  is  termed  the 


Lobulus 


Fig.    102. — The  Pinna. 


270  HEAD  AND  NECK 

tragus,  whilst  a  similar  eminence  behind  and  below  the  meatus 
receives  the  name  of  the  antitragus.  The  notch  between 
these  two  prominences  is  termed  the  incisura  intertragica.  But 
it  will  be  noted  that  the  upper  end  of  the  ahtihelix  bifurcates, 
and  in  this  way  two  fossae  are  marked  off  from  each  other;  one 
— the  fossa  of  the  helix,  or  scaphoid  fossa — is  placed  between 
the  helix  and  the  antihelix,  and  the  other — the  fossa  of  the 
antihelix,  or  triangular  fossa  —  is  situated  between  the  two 
diverging  terminal  limbs  of  the  antihelix. 

The  pinna  may  now  be  dissected.  It  consists  of  a  thin  plate  of  yellow 
fibro-cartilage,  covered  by  integument.  It  is  fixed  in  position  by  certain 
ligaments,  and  possesses  two  sets  of  feeble  muscles — viz.,  one  group 
termed  the  extrinsic  muscles,  passing  to  the  cartilage  from  the  aponeurosis 
of  the  occipito-frontalis  and  the  mastoid  process,  and  a  second  group  in 
connexion  with  the  cartilage  alone,  and  therefore  called  the  intrinsic 
micscles. 

T  .  f  Anterior. 

Ligaments,     .  .  .  •         r>    <.     • 

fa  '  ^  rostenor. 

fAttrahens.    \ 

Extrinsic  muscles, -J  Attollens.     /-Already  examined,  p.  107. 

[Retrahens.  J 

f  Musculus  helicis  major.    ~\ 

Museums  helicis  minor.     I  Upon  the  outer  face  of  the 

T   .  •     •  ,        f  Musculus  tragdeus.  |      cartilage. 

Intrinsic  muscles,  J  ,,         ,  p.  b 

'      Musculus  antitragicus.      J 

Musculus  transversus.       )  Upon    the    cranial   face    of 

^Musculus  obliquus.  /     the  cartilage. 

The  skin  should  be  carefully  removed  from  the  entire  extent  of  the 
external  auricle.  Particular  care  must  be  taken  in  the  regions  where  the 
intrinsic  muscles  are  placed. 

The  auricular  cartilage  extends  throughout  the  entire  pinna,  with  the 
exception  of  the  lobule  and  the  portion  between  the  tragus  and  the  helix. 
These  portions  are  composed  merely  of  integument,  fatty  tissue,  and 
condensed  connective  tissue.  *  The  shape  of  the  cartilage  corresponds  with 
that  of  the  pinna  itself.  It  shows  the  same  elevations  and  depressions, 
and  by  its  elasticity  it  serves  to  maintain  the  form  of  the  auricle.  But  it 
also  enters  into  the  formation  of  the  cartilaginous  or  outer  portion  of  the 
external  auditory  meatus.  By  its  inner  margin  this  part  of  the  cartilage 
is  firmly  fixed  by  fibrous  tissue  to  the  rough  outer  edge  of  the  auditory 
process  of  the  temporal  bone,  but  it  does  not  form  a  complete  tube.  It  is 
deficient  above  and  in  front,  and  here  the  tube  of  the  meatus  is  completed 
by  tough  fibrous  membrane,  which  stretches  between  the  tragus  and  the 
commencement  of  the  helix. 

In  a  successful  dissection  of  the  cartilage  of  the  pinna,  two  other  points 
will  attract  the  attention  of  the  student.  The  first  is  a  deep  slit,  which 
passes  upwards  so  as  to  separate  the  lower  part  of  the  cartilage  of  the 
helix,  termed  the  processus  helicis  caudatus,  from  the  cartilage  of  the  anti- 
tragus ;  the  second  is  a  sharp  spur  of  cartilage  which  projects  forward  from 
the  helix  at  the  level  of  the  upper  margin  of  the  zygoma.  This  is  termed 
the  spina  helicis. 

The   ligaments    of  the    auricle    are    two   in   number.     The   anterior 


DISSECTION  OF  THE  FACE 


271 


aurictdar  ligament  stretches  from  the  spine  of  the  helix  to  the  root  of  the 
zygomatic  process.  The  posterior  aurictdar  ligament  will  be  found  under 
cover  of  the  retrahens  auriculam.  It  is  stronger  than  the  preceding,  and 
extends  from  a  slight  depression  on  the  cranial  aspect  of  the  concha  to  the 
mastoid  process. 

The  intrinsic  muscles  of  the  pinna  must  be  sought  for  with  care.  The 
two  muscles  of  the  helix,  the  tragicus  and  the  antitragicus,  are  placed 
upon  the  outer  face  of  the  cartilage.  The  transversus  and  the  obliquus  lie 
upon  the  cranial  surface  of  the  pinna. 

The  musculus  antitragicus  is  the  best-marked  member  of  the  outer 
group.  It  lies  upon  the  outer  surface  of  the  antitragus,  and  its  fibres  pass 
obliquely  upwards  and  backwards.  Some  fasciculi  can  be  traced  to  the 
processus  helicis  caudatus. 

The  mnsculus  tragicus  is  a  minute  bundle  of  short  vertical  fibres 
situated  upon  the  outer  surface  of  the  tragus.  When  well  developed  a 
slender  fasciculus  may  sometimes  be  observed  to  pass  upwards  from  it  to 
the  fore-part  of  the  helix,  where  it  gains  insertion  into  the  spine  of  the  helix. 

The  mnsculus  helicis  major  is  a  well-marked  band,  which  springs  from 
the  spina  helicis,  and  extends  upwards  upon  the  fore-part  of  the  helix,  to 
be  inserted  into  the  skin  which  covers  it. 

The  musculus  helicis  minor  is  a  minute  bundle  of  fleshy  fibres  which  is 
placed  upon  the  crus  helicis  as  it  crosses  the  bottom  of  the  concha. 

The  musculus  transversus  auriculce  is  found  upon  the  cranial  aspect  of 
the  pinna.  It  is  generally  the  most  strongly  developed  muscle  of  the  series, 
and  it  consists  of  fibres  bridging  across  the  hollow  which,  on  this  aspect  of 
the  auricle,  corresponds  to  the  antihelix. 

The  musculus  obliqtius  auriculce  is  composed  of  some  vertical  fasciculi 
bridging  across  the  depression  which  corresponds  to  the  eminence  of  the 
lower  limb  of  the  antihelix. 

Eyelids. — The  following  strata  will  be  exposed  in  each 
eyelid  as  the  student  dissects  from  the  surface  towards  the 
conjunctiva  lining  its  deep  aspect : — 


Upper  Lid. 

Lower  Lid. 

1.  Integument. 

2.  Palpebral  part  of  the  orbicularis 

palpebrarum. 

3.  The  tarsus,  the  palpebral  liga- 

ment, and  the  expanded  ten- 
don   of  the    levator  palpebral 

1.  Integument. 

2.  Palpebral  part  of  the  orbicularis 

palpebrarum. 

3.  The   tarsus   and   the   palpebral 

ligament. 

supenons. 
4.   Conjunctiva. 

4.   Conjunctiva. 

In  addition  to  these  structures,  two  ligaments  named  the 
internal  and  external  tarsal  ligaments  will  be  noticed.  They 
attach  the  tarsal  plates  to  the  inner  and  outer  margins  of 
the  orbit. 


The  dissection  should  be  carried  on  in  both  eyelids  at  the  same  time. 


272  HEAD  AND  NECK 

Integument  and  Orbicularis. — These  strata  have  already 
been  examined,  and  the  skin  has  been  reflected.  The 
palpebral  part  of  the  orbicularis  muscle  in  each  lid  forms  a 
thin  layer  of  arching  muscular  fibres  loosely  connected  with 
the  integument  by  some  lax  areolar  tissue.  A  fasciculus, 
somewhat  thicker  than  the  others  (ciliary  bundle  or  muscle  of 
Riolan)  lies  along  the  free  margin  of  each  lid,  close  to  the 
bases  of  the  eyelashes. 

Dissection. — The  entire  orbicularis  muscle  may  now  be  thrown  inwards. 
This  will  show  very  clearly  the  origin  of  its  muscular  fibres  at  the  inner 
margin  of  the  orbit  (p.  253).  In  raising  the  palpebral  part  great  care 
must  be  taken  to  preserve  the  palpebral  vessels  and  nerves,  and  at  the 
same  time  to  avoid  injury  to  the  palpebral  ligament. 

Tarsi. — The  removal  of  the  palpebral  part  of  the  orbicularis 
brings  into  view  the  palpebral  ligaments  and  the  tarsal  plates. 
These  lie  in  the  same  morphological  plane,  and  they  constitute 
the  ground-work  of  the  eyelids. 

The  tarsi  are  two  thin  plates  of  condensed  connective  tissue 
placed  one  in  each  eyelid,  so  as  to  occupy  an  area  immediately 
adjoining  its  free  margin.  They  differ  very  materially  from 
each  other.  The  superior  tarsal  plate  is  much  the  larger  of 
the  two,  and  presents  the  figure  of  a  half  oval.  Its  deep 
surface  is  intimately  connected  writh  the  subjacent  conjunctiva, 
whilst  its  superficial  surface  is  clothed  by  the  orbicularis  muscle, 
and  is  in  relation  to  the  roots  of  the  eyelashes.  Its  superior 
border  is  thin,  convex,  and  continuous  writh  the  tendinous 
expansion  of  the  levator  palpebral  superioris.  The  inferior 
border  of  the  tarsal  plate  is  thickened  and  straight,  and  the 
integument  adheres  firmly  to  it. 

The  inferior  tarsal  plate  is  a  narrow  strip  which  is  similarly 
placed  in  the  lower  lid. 

Meibomian  Follicles  (glandular  tarsales). — At  this  stage 
the  attention  of  the  student  cannot  fail  to  be  attracted  by 
the  Meibo77iian  follicles,  which  are  placed  on  the  deep  surfaces 
of  the  tarsal  plates.  To  the  naked  eye  they  appear  as  closely 
placed,  parallel,  yellow,  granular-looking  streaks,  which  run  at 
right  angles  to  the  free  margins  of  the  lids.  They  are  more 
numerous  and  of  greater  length  in  the  upper  lid,  and,  being 
lodged  in  furrows  on  the  deep  surface  of  the  tarsal  plates, 
they  are  distinctly  visible  upon  both  aspects  of  these,  even 
while  the  conjunctiva  is  in  position.  The  ducts  open  upon 
the  free  margin  of  each  lid  behind  the  eyelashes,  and  by  the 


DISSECTION   OF  THE  FACE 


273 


aid  of  a  magnify ing-glass  they  can  be  seen  as  round  orifices 
placed  in  a  single  row. 

The  mouths  of  these  glands  can  be  well  demonstrated  by 
squeezing  the  eyelid  between  the  finger  and  thumb,  when 
the  greasy  secretion  of  the  glands  will  be  pressed  out. 


Margin  of  the  upper  eye- 
lid with  openings  of 
Meibomian  ducts 


Papilla  lachrymalis  with 
punctum  lachrymale  on 
the  summit 


Plica  semilunaris 
Caruncula  lachrymalis 
Papilla  lachrymalis 

Meibomian  openings 


Meibomian  glands 
shining  through  the 
conjunctiva 


Fig.  103. — Eyelid  slightly  everted  to  show  the  Conjunctiva  (enlarged). 


In  front  of  the  bases  of  the  eyelashes,  between  them  and  the  ciliary 
muscle,  are  two  or  three  rows  of  modified  sweat-glands.  These  are 
called  the  glands  of  Moll,  and  when  their  ducts  become  occluded  the 
condition  familiarly  known  as  stye  results. 

Palpebral  Ligaments. — These  are  two  broad  membranous 
sheets  which  extend  into  the  basal  portions  of  the  eyelids 
from  the  upper  and  lower  margins  of  the  orbital  opening. 
They  form  an  incomplete  membranous  diaphragm  around 
the  circumferential  part  of  the  orbital  opening,  termed  the 
sephcm  orbitale.  The  superior  ligament  blends  along  the 
orbital  arch  with  the  pericranium  clothing  the  frontal  bone, 

VOL.    II   —18 


274 


HEAD  AND  NECK 


and  with  the  periosteum  lining  the  roof  of  the  orbit,  whilst 
inferiorly  it  blends  with  the  expanded  tendon  of  the  levator 
palpebral  superioris.  The  inferior  ligament  is  continuous 
on  the  one  hand  with  the  lower  margin  and  anterior  aspect 
of  the  lower  tarsal  plate,  and  on  the  other  with  the  periosteum 
of  the  face  and  the  floor  of  the  orbit.  Towards  the  inner 
canthus,  where  the  eyelids  are  supported  by  the  internal 
tarsal  ligament,  the  palpebral  ligaments  become  thin  and 
delicate,  and  receive  attachment  to  the  lachrymal  bone  behind 
the  lachrymal  sac. 

Tarsal  Ligaments. — The  palpebral  ligaments  fix  the  tarsi 

Frontal  bone 
Orbicularis  palpebrarum 


Superior  palpebral  ligament  — 

Superior  conjunctival  fornix 
Superior  tarsal  plate 


Conjunctival  recess  — 


Inferior  conjunctival  fornix 
Inferior  palpebral  ligament^ 

Fig.  104. — Diagram  of  the  Structure  of  the  Eyelids. 

to  the  upper  and  lower  margins  of  the  orbit ;  the  tarsal 
ligaments  attach  the  tarsi  to  the  outer  and  inner  orbital 
margins. 

The  external  tarsal  ligament  is  a  narrow  band  of  no  great 
strength,  which  springs  from  the  malar  bone  where  this 
forms  the  outer  margin  of  the  orbit  and  proceeds  inwards. 
At  the  outer  canthus,  it  divides  into  two  pieces,  an  upper 
and  a  lower,  which  are  attached  to  the  tarsal  plates.  This 
ligament  is  merely  a  thickening  of  the  palpebral  ligaments 
where  they  are  continuous  with  each  other  at  the  outer 
margin  of  the  orbit. 

The  internal  tarsal  ligame?it  is  a   much   more   important 


DISSECTION  OF  THE  FACE 


275 


structure.  It  has  a  double  function  to  perform,  viz.,  (1)  to 
serve  as  a  tendon  of  origin  for  the  orbicularis  muscle,  and 
(2)  to  fix  the  tarsi  to  the  inner  margin  of  the  orbit.  To 
obtain  a  satisfactory  view  of  it,  the  muscular  fibres  which 
spring  from  its  upper  and  lower  margins  must  be  completely 
removed. 

The    internal  tarsal  ligament    is    a    strong    fibrous    band 
which  springs  from  the  nasal  process  of  the  superior  maxil- 


Tendon  of  levator 
palpebrae  superioris 


Superior  palpebral 

ligament  ""■■* 

Palpebral  branch  of 
lachrymal  nerve" 

Superior  tarsus  -  _ 


External  tarsal 

ligament  / 


Inferior  palpebral 
ligament 


Infra-orbital  nerve 


Supra-orbital  nerve 
m£&    \    Supra-trochlear  nerve 
Superciliary  ridge 


m     Infra-trochlear  nerve 


Lachrymal  sac 

Internal  tarsal 
ligament 


Inferior  tarsus 


Fig.   105. — Dissection  of  the  Right  Eyelid.      The  orbicularis  palpebrarum  has 
been  completely  removed. 

lary  bone  immediately  in  front  of  the  lachrymal  groove.  It 
passes  outwards  and  divides  at  the  inner  canthus  into  two 
diverging  portions  which  are  attached  one  to  each  tarsal 
plate. 

The  superficial  surface  of  the  internal  tarsal  ligament  is 
covered  by  the  integument ;  the  deep  surface  crosses  the 
lachrymal  sac  a  short  distance  above  its  centre  and  gives  to 
it  a  fibrous  expansion,  which  is  attached  behind  to  the 
posterior  margin  of  the  lachrymal  groove. 

Dissection. — The  dissection  of  the   lower  lid   is  now  completed,   but  in 
the  case  of  the  upper   eyelid   the  dissector   must   proceed   to  detach  care- 


276  HEAD  AND  NECK 

fully  the  superior  palpebral  ligament  from  the  margin  of  the  orbit,  and 
throw  it  downwards  towards  the  tarsal  plate.  This  will  expose  the  ex- 
panded tendon  of  the  levator  palpebrae  superioris. 

Levator  Palpebrse  Superioris. — This  muscle  arises  within 
the  cavity  of  the  orbit.  Its  tendon  spreads  out  into  a  wide 
expansion  which  enters  the  basal  part  of  the  upper  eyelid. 
It  is  impossible  in  the  course  of  an  ordinary  dissection  to 
make  out  all  the  very  intricate  connexions  of  this  tendon. 
It  splits  into  three  laminae.  Of  these  the  superficial  layer 
blends  with  the  superior  palpebral  ligament,  and  is  carried 
forwards  above  the  tarsal  plate  to  the  deep  surface  of  the 
palpebral  part  of  the  orbicularis  muscle.  The  intermediate 
stratum,  largely  composed  of  involuntary  muscular  fibres,  is 
inserted  into  the  upper  border  of  the  tarsal  plate ;  whilst 
the  deepest  lamina  is  attached  to  the  fornix  conjunctivae 
superior  (Fig.  104). 

Vessels  and  Nerves  of  the  Eyelids.  —  At  the  inner 
canthus  two  arteries  —  the  palpebral  branches  of  the  oph- 
thalmic artery — appear  and  run  outwards  in  the  upper  and 
lower  lids.  At  the  outer  margin  of  the  orbit,  one'  or 
more  branches  of  the  lachrymal  artery  pierce  the  palpebral 
ligament,  and  anastomose  with  the  palpebral  arteries.  An 
arterial  arch  (arcus  tarseus)  is  thus  formed  close  to  the 
margin  of  each  eyelid,  between  the  orbicularis  muscle  and 
the  tarsal  plate. 

The  veins  run  inwards  towards  the  root  of  the  nose,  and 
open  into  the  frontal  and  angular  veins. 

The  nerves  are  more  numerous,  and  come  from  a  number 
of  different  sources.  The  motor  filaments  for  the  palpebral 
part  of  the  orbicularis  proceed  from  the  facial  nerve,  and 
enter  the  lids  at  the  outer  margin  of  the  orbit.  The  sen- 
sory twigs  for  the  upper  lid  come  from  the  lachry77ial,  supra- 
orbital, supra-trochlear,  and  infra-trochlear  nerves,  whilst  the 
lower  lid  is  supplied  by  branches  from  the  infra-orbital 
nerve. 

Lachrymal  Apparatus. — The  following  structures  are  in- 
cluded under  this  heading  : — 

1.  The  lachrymal  gland  and  its  ducts. 

2.  The  lachrymal  canals. 

3.  The  lachrymal  sac  and  the  nasal  duct. 

4.  The  tensor  tarsi  muscle. 

The  Lachrymal  Gland  lies  within  the  orbit,  in  the  hollow 


DISSECTION  OF  THE  FACE 


277 


Lachrymal  canal  Lachrymal  sac 


Op 


on  the  roof  of  this  cavity,  at  the  inner  side  of  the  external 
angular  process  of  the  frontal  bone.  The  fore-part  of  the 
gland  projects  slightly  beyond  the  orbital  margin,  and  rests 
upon  the  conjunctiva  of  the  upper  eyelid,  as  it  is  reflected 
from  the  lid  on  to  the  eyeball.  If  the  gland  be  now  raised 
gently  and  the  point  of  the  knife  carried  carefully  up  and 
down  through  the  connective  tissue  under  it,  several  ex- 
ceedingly delicate  ducts,  like  fine  threads,  will  be  seen  pro- 
ceeding from  the  gland. 
These  vary  greatly  in 
number,  and  they  open 
upon  the  under  surface 
of  the  conjunctiva  of 
the  upper  lid,  in  the 
neighbourhood  of  the 
fornix  or  the  reflection 
of  this  membrane  upon 
the  anterior  surface  of 
the  globe  of  the  eye. 

The  tears  secreted 
by  the  lachrymal  gland 
thus  reach  the  under  i»ferior 
surface  of  the  upper  lid, 
and  by  the  involuntary 
closure  of  the  lids  in 
winking  they  are  washed 
over  the  exposed  part 
of  the  eyeball  and  at 
the  same  time  directed 
inwards  towards  the 
inner  canthus.  From 
the  lacus  lachrymalis  they  are  drained  away  by  the  lachrymal 
canals. 

The  Lachrymal  Canals  (ductus  lacrimales)  have  in  a 
measure  been  already  examined.  The  dissector  has  noted 
the  punda  lachrymalia,  or  the  mouths  of  these  minute  canals, 
upon  the  margins  of  the  eyelids  at  the  inner  canthus,  and  he 
has  endeavoured  to  determine  the  course  pursued  by  each, 
by  the  introduction  of  a  bristle.  The  upper  canal  at  first 
ascends  for  a  short  distance,  whilst  the  lower  one  descends, 
and  then,  changing  their  direction  suddenly,  they  both  run 
inwards  in  relation  to  the  upper  and  lower  margins  of  the 
11— 18  a 


FlG.  106. — Diagram  of  the  Lachrymal  Ducts 
and  Sac,  and  of  the  Nasal  Duct.    (Gegenbaur. ) 


278  '  HEAD  AND  NECK 

internal  tarsal  ligament.  They  open  close  together  into  the 
outer  and  anterior  aspect  of  the  lachrymal  sac  at  a  point 
slightly  above  its  centre.  The  upper  canal  is  the  smaller  and 
longer  of  the  two,  and  it  inclines  downwards  as  well  as  inwards 
to  reach  the  lachrymal  sac ;  the  lower  canal  is  nearly  hori- 
zontal in  direction. 

The  Lachrymal  Sac  (saccus  lacrimalis)  is  the  blind  upper 
and  somewhat  expanded  part  of  the  passage  which  conducts 
the  tears  to  the  nasal  cavity.  It  is  lodged  in  the  deep 
lachrymal  groove  in  the  fore-part  of  the  inner  wall  of  the 
orbit,  and  it  is  crossed  in  front,  a  short  distance  above  its 
middle,  by  the  internal  tarsal  ligament,  from  the  deep  surface 
of  which  it  receives  a  fibrous  expansion.  The  lachrymal 
canals  open  into  it  under  cover  of  this  ligament. 

The  nasal  duct  is  the  term  which  is  applied  to  the  lower 
part  of  the  same  passage.  It  descends  in  the  bony  nasal 
canal,  and  opens  into  the  fore-part  of  the  inferior  meatus  of 
the  nose.     In  length  it  measures  about  half  an  inch. 

Dissection. — In  cases  where  the  dissector  is  dealing  with  undissected 
eyelids,  the  tensor  tarsi  muscle  can  be  well  exposed  from  the  deep  aspect 
of  the  lids  by  dividing  them  vertically  through  the  middle,  and  turning  the 
inner  portions  upwards  and  downwards.  The  removal  of  the  conjunctiva 
at  the  inner  canthus  will  bring  it  into  view. 

The  Tensor  Tarsi  Muscle  is  a  muscular  slip  which  can 
now  be  seen  arising  from  the  crest  of  the  lachrymal  bone 
behind  the  lachrymal  sac.  It  is  simply  a  deep  portion  of  the 
orbicularis  palpebrarum,  with  which  it  blends  on  the  outer 
side  of  the  lachrymal  sac.  The  lachrymal  canaliculi  and 
lachrymal  sac  are  thus  enclosed  in  muscular  fibres. 

Dissection. — The  cartilaginous  part  of  the  nose  should  now  be  examined 
by  stripping  off  the  compressor  naris  muscle  and  the  remains  of  the 
integument. 

Nasal  Cartilages.  —  In  addition  to  the  septal  cartilage, 
which  will  be  more  appropriately  studied  in  the  dissection  of 
the  nasal  chambers,  two  cartilaginous  plates  will  be  found 
upon  each  side.     These  are  : — 

1.  The  upper  lateral  cartilage. 

2.  The  cartilage  of  the  aperture. 

The  upper  lateral  cartilage  is  a  triangular  plate  which  by 
its  posterior  margin  is  attached  to  the  lower  border  of  the 
nasal  bone  and  the  upper  part   of  the  sharp  margin   of  the 


DISSECTION   OF  THE   FACE 


279 


nasal  notch  of  the  superior  maxillary  bone.  In  the  mesial 
plane  this  cartilage  becomes  continuous  with  its  fellow  of  the 
opposite  side,  and  also  with  the  subjacent  anterior  border  of 
the  septal  cartilage  of  the  nose.  Below,  there  is  a  slight 
interval  between  the  two  lateral  cartilages,  in  which  is  seen 
the  margin  of  the  nasal  septal  cartilage.  The  inferior  border 
of  the  lateral  cartilage  is  connected  with  the  outer  part  of 
the  cartilage  of  the  aperture  by  some  dense  fibrous  tissue. 

The  cartilage  of  the  aperture  is  bent  upon  itself  and  folded 
round  the  orifice  of  the  nostril  in  front  and  laterally, — 
posteriorly  it  is  deficient. 
The  outer  part  is  of  an 
oval  form,  and  does  not 
reach  down  to  the  margin 
of  the  nostril,  nor  back- 
wards as  far  as  the  nasal 
notch  of  the  superior 
maxilla.  The  interval 
between  it  and  the  bone 
is  filled  in  by  fibrous 
tissue  in  which  one  or  two 
small  islands  of  cartilage 
(cartilagines  minores  vel 
sesamoideae)  appear.  In 
front,  the  bent  part  of 
cartilage  comes  into  con- 
tact with  its  neighbour  and  forms  the  point  of  the  nose. 
Internally,  the  inner  part  of  the  cartilage  is  in  the  form  of  a 
narrow  strip  which  lies  upon  the  lower  part  of  the  septal 
cartilage,  and  projects  slightly  below  it  so  as  to  support  the 
margin  of  the  nostril  upon  this  side.  Its  extremity  is  turned 
slightly  outwards. 


Nasal  nerve 


Lateral  cartilage 


Sesamoid  cartilages 
Cartilage  of  the 
aperture 


Fig.  107. — Cartilages  of  the  Nose. 


THE   TEMPORAL  AND   PTERYGO-MAXILLARY 

REGIONS. 

Under  this  heading  are  grouped  the  parts  which  are  dis- 
sected in  the  temporal  and  zygomatic  fossae  of  the  skull. 

Dissection. — The  structures  which  cover  and  lie  superficial  to  the  tem- 
poral fascia  have  already   been  examined   in   the  dissection  of  the  scalp 
(pp.  109,  no). 
n—186 


28o  HEAD  AND  NECK 

Throw  the  temporal  part  of  the  orbicularis  palpebrarum  forwards  ;  pre- 
serve the  middle  temporal  artery,  and  the  temporal  branch  of  the  temporo- 
malar  nerve,  both  of  which  pierce  the  temporal  fascia  ;  turn  downwards 
the  other  vessels  and  nerves  which  lie  on  the  temporal  fascia,  and  remove 
what  remains  of  the  temporal  part  of  the  epicranial  aponeurosis  and  of  the 
two  upper  ear  muscles.     The  temporal  fascia  is  in  this  manner  laid  bare. 

Temporal  Fascia  (fascia  temporalis).  — The  temporal  fascia 
is  a  strong  glistening  aponeurosis  which  is  stretched  over  the 
temporal  fossa,  and  binds  down  the  muscle  of  the  same  name. 
Its  upper  margin  is  attached  to  the  upper  of  the  two  curved 
lines  which  constitute  the  temporal  ridge  on  the  lateral  aspect 
of  the  skull,  and  in  front  to  the  temporal  crest  of  the  frontal 
bone.  As  it  approaches  the  zygomatic  arch,  it  splits  into 
two  laminae,  which  are  separated  from  each  other  by  a  narrow 
interval  filled  with  fat.  These  are  attached  to  the  outer  and 
inner  margins  of  the  upper  border  of  the  zygomatic  arch,  and 
to  the  posterior  border  of  the  malar  bone.  They  can  readily 
be  demonstrated  by  dividing  the  superficial  layer  close  to  its 
attachment,  and  throwing  it  upwards ;  by  the  handle  of  the 
knife  the  attachment  of  the  deep  layer  can  then  be  made  out. 
In  the  upper  part  of  its  extent,  the  temporal  fascia  is  com- 
paratively thin,  and  the  fibres  of  the  subjacent  muscle  may 
be  seen  shining  through  it ;  below,  it  is  thicker,  and  owing  to 
the  fat  which  is  interposed  between  its  laminae  it  becomes 
perfectly  opaque. 

Dissection. — The  masseter  rfiuscle  must  now  be  thoroughly  cleaned. 
To  do  this  effectually,  it  will  be  necessary  to  divide  the  trunk  of  the  facial 
nerve  immediately  beyond  the  point  where  it  gives  off  the  branches  to  the 
digastric  and  stylo-hyoid  muscles,  and  throw  it  forwards,  with  the  various 
branches  which  spring  from  it,  towards  the  buccal  region.  The  transverse 
facial  artery  must  be  also  turned  backwards.  The  dissector  will  recollect 
that  he  has  previously  removed  from  the  surface  of  the  masseter  a  forward 
prolongation  of  the  parotid  gland,  the  socia  parotidis,  Stenson's  duct,  twigs 
from  the  great  auricular  nerve,  scattered  fibres  of  the  platysma,  and  the 
origin  of  the  risorius  muscle. 

Masseter. — The  masseter  is  a  massive  quadrate  muscle 
which  lies  upon  the  ascending  ramus  of  the  lower  jaw.  Its 
fibres  are  arranged  in  two  sets — a  superficial  and  a  deep. 
The  superficial  part  of  the  muscle  arises  from  anterior  two- 
thirds  of  the  lower  border  of  the  zygomatic  arch,  and  its 
fasciculi  are  directed  downwards  and  backwards.  The  deep 
part  springs  from  the  whole  length  of  the  inner  aspect  of  the 
zygomatic  arch,  and  also  from  the  posterior  third  of  its  lower 
border.      Its  fibres   proceed  downwards  and  forwards.     The 


TEMPORAL  AND  PTERYGOID  REGIONS     281 

only  portion  of  the  deep  part  which  appears  on  the  surface  is 
a  small  piece  at  the  upper  and  back  part  of  the  muscle. 
The  masseter  is  inserted  into  the  outer  surface  of  the  ascend- 
ing ramus  of  the  mandible,  over  an  area  which  extends  down- 
wards to  the  angle,  and  upwards  so  as  to  include  the  outer 
aspect  of  the  coronoid  process. 

Dissection. — A  dissection  must  now  be  undertaken  to  display  the 
temporal  muscle,  and  at  the  same  time  expose  the  nerve  and  artery  of 
supply  to  the  masseter.  Begin  by  dividing  the  temporal  fascia  along  the 
upper  border  of  the  zygomatic  arch.  It  may  then  be  thrown  upwards  and 
completely  removed.  The  middle  temporal  artery  and  the  temporal 
branch  of  the  temporo-malar  nerve  which  pierce  it  must  be  disengaged 
from  it  and  preserved.  The  zygomatic  arch  with  the  attached  masseter 
must  next  be  thrown  down  by  dividing  the  bony  arch  in  front  and  behind 
the  origin  of  the  muscle.  First  make  use  of  the  saw,  and  then  complete 
the  division  by  means  of  the  bone  pliers.  The  posterior  cut  should  be 
made  immediately  in  front  of  the  glenoid  fossa,  and  the  head  of  the  lower 
jaw  ;  the  anterior  cut  must  extend  obliquely  through  the  malar  bone,  from 
the  extreme  anterior  end  of  the  upper  margin  of  the  arch,  downwards  and 
forwards  to  the  point  where  the  lower  margin  meets  the  malar  process  of 
the  superior  maxillary  bone.  In  this  way  the  whole  of  the  masseteric 
origin  is  included  between  the  incisions,  and  the  arch  with  the  attached 
muscle  may  be  readily  thrown  downwards  towards  the  angle  of  the  lower 
jaw.  The  fleshy  origin  of  the  deep  portion  of  the  masseter  from  the  inner 
surface  of  the  zygomatic  arch  can  now  be  seen,  and  frequently  the  dissection 
is  complicated  by  a  number  of  fibres  from  the  temporal  muscle  joining  this 
part  of  the  masseter.  In  turning  the  masseter  down,  great  care  must  be 
taken  not  to  injure  its  nerve  and  artery  of  supply.  These  pass  outwards 
through  the  sigmoid  notch,  between  the  neck  of  the  lower  jaw  and  the 
posterior  margin  of  the  temporal  muscle.  When  they  are  exposed  and 
cleaned,  they  must  be  divided  in  order  that  the  muscle  may  be  fully  re- 
flected. On  no  account  detach  the  masseter  from  the  angle  of  the  jaw. 
The  temporal  muscle  may  now  be  cleaned. 

Temporal  Muscle  (musculus  temporalis). — The  temporal 
muscle  is  fan-shaped.  It  arises  from  the  entire  extent  of  the 
temporal  fossa  by  an  origin  reaching  upwards  as  high  as  the 
lower  of  the  two  lines  which  constitute  the  temporal  ridge, 
and  downwards  as  low  as  the  infra-temporal  crest  on  the  great 
wing  of  the  sphenoid.  It  also  receives  additional  fibres  from 
the  deep  surface  of  the  temporal  fascia  which  covers  it. 
From  this  broad  origin  the  fasciculi  of  the  temporal  muscle 
converge  towards  the  coronoid  process  of  the  lower  jaw. 
The  anterior  fibres  descend  vertically,  the  posterior  fibres  at 
first  pursue  a  nearly  horizontal  course,  whilst  the  intermediate 
fasciculi  proceed  with  varying  degrees  of  obliquity.  As  it 
approaches  its  insertion,  a  tendon  is  developed  upon  its 
superficial  aspect,  and  this  is  inserted  into  the  summit  and 


282  HEAD  AND  NECK 

anterior  edge  of  the  coronoid  process  of  the  mandible.  The 
deep  part  of  the  muscle  remains  fleshy,  and  gains  attachment 
to  the  inner  surface  of  the  same  bony  prominence  by  an  inser- 
tion which  reaches  as  low  down  as  the  point  where  the  anterior 
margin  of  the  ramus  merges  into  the  body  of  the  mandible. 

Dissection. — The  next  step  in  the  dissection  of  this  region  consists  in 
separating  the  coronoid  process  from  the  mandible,  and  turning  it  upwards 
with  the  attached  temporal  muscle.  A  very  oblique  cut  is  required  ;  it 
should  extend  from  the  centre  of  the  sigmoid  notch  above,  downwards  and 
forwards,  to  the  point  where  the  anterior  margin  of  the  ascending  ramus 
meets  the  body  of  the  mandible.  First  use  the  saw,  and  then  complete 
the  division  with  the  bone  pliers.  The  long  buccal  nei"ve  and  its  companion 
artery  are  in  a  position  of  danger  during  this  dissection,  and  must  be  care- 
fully guarded.  They  proceed  downwards  and  forwards  under  cover  of  the 
lower  part  of  the  temporal  muscle,  and  not  infrequently  the  nerve  will  be 
found  traversing  its  substance.  The  coronoid  process  and  the  temporal 
muscle  should  be  thrown  well  upwards,  and  the  muscular  fibres  separated 
by  the  handle  of  the  knife  from  the  bone  forming  the  lower  part  of  the 
temporal  fossa.  This  will  bring  into  view  the  deep  temporal  nerves  and 
arteries  as  they  ascend  between  the  cranial  wall  and  the  muscle.  This  is 
the  time  also  to  follow  the  middle  temporal  artery.  It  will  be  noticed  to 
give  branches  to  the  muscle  and  extend  upwards  upon  the  squamous  part 
of  the  temporal  bone.  The  temporal  branch  of  the  temporo-malar  nerve 
should  likewise  be  traced  to  the  point  where  it  emerges  from  the  minute 
aperture  on  the  temporal  surface  of  the  malar  bone.  At  this  point  it  lies 
under  cover  of  the  temporal  muscle. 

The  pterygoid  region  may  now  be  fully  opened  up  by  removing  a 
portion  of  the  ascending  ramus  of  the  mandible.  Two  horizontal  cuts 
must  be  made — one  through  the  neck  of  the  mandible,  and  the  other  im- 
mediately above  the  level  of  the  inferior  dental  foramen.  To  find  the 
level  of  the  latter,  the  handle  of  the  forceps  should  be  thrust  forwards 
between  the  ramus  and  the  subjacent  soft  parts,  and  carried  downwards. 
Its  progress  will  soon  be  arrested  by  the  entrance  of  the  inferior  dental 
vessels  and  nerve  into  the  foramen,  and  the  lower  border  of  the  instrument 
will  correspond  with  the  line  along  which  the  bone  should  be  cut.  Both 
incisions  should  be  made  with  the  saw,  until  the  outer  table  of  the  bone  is 
cut  through,  and  then  the  bone  pliers  may  be  employed  to  complete  the 
division. 

Parts  displayed  by  the  above  Dissection. — When  the  fat 
and  areolar  tissue  are  removed,  the  pterygoid  muscles  will 
come  into  view.  The  external  pterygoid  will  be  recognised 
from  its  extending  horizontally  backwards  to  the  neck  of  the 
mandible.  The  internal  pterygoid,  embracing  the  anterior 
part  of  the  external  pterygoid  muscle  between  its  two  heads 
of  origin,  proceeds  downwards  and  backwards  upon  the  deep 
surface  of  the  ramus  of  the  mandible.  It  bears  very  much 
the  same  relation  to  the  inner  aspect  of  the  ascending  ramus 
that  the  masseter  presents  to  its  outer  surface.  The  great 
blood  vessel  of  the  space — the  internal  maxillary  artery — pro- 


TEMPORAL  AND  PTERYGOID  REGIONS     283 

ceeds  forwards  upon  (frequently  under  cover  of)  the  external 
pterygoid  muscle.  The  nerves  will  also  be  observed  to  be 
placed  in  close  relationship  to  the  same  muscle.  Thus, 
emerging  from  between  its  upper  border  and  the  cranial  wall 
at  the  level  of  the  infratemporal  crest  are  the  masseteric  and 
the  two  deep  temporal  nerves ;  appearing  from  under  cover  of 


Internal 

maxillary 

Posterior 

superior  dental 

Long 
buccal  nerve 
and  artery 


Temporal  muscle 


Deep  temporal  artery 


Deep  temporal  nerve 
Deep  temporal  artery 

/Deep  temporal  nerve 
Masseteric  nerve 


i     Superficial  temporal  artery 
Auriculo-temporal  nerve 


External  pterygoid 


Middle  meningeal  artery 


Mastoid  process 
—  External  carotid 

Small  meningeal  artery 


r.i       \        srnau  meningeal  a 
\       Inferior  dental  artery 


Huccinator 

Fig.  108. 


Mylo-hyoid  artery  and  nerve 
Inferior  dental  nerve 
Lingual  nerve 
Internal  pterygoid  muscle 

-Dissection  of  the  Pterygo-maxillary  Space. 


its  lower  border  are  the  mandibular  or  inferior  dental  and  the 
lingual  nerves ;  whilst  the  auriculo-temporal  nerve  is  related  to 
it  behind,  and  the  long  buccal  nerve  in  front.  The  former 
passes  backwards  under  cover  of  its  insertion,  and  appears 
behind  the  temporo-maxillary  joint,  and  the  long  buccal  either 
pierces  it  or  emerges  from  between  its  two  heads  of  origin. 
The  internal  lateral  ligament  of  the  lower  jaw  will  likewise 
be  seen.  It  is  the  thin  strip  of  membrane  upon  which  the 
inferior  dental  or  mandibular  nerve  rests. 


284  HEAD  AND  NECK 

External  Pterygoid  Muscle  (musculus  pterygoideus  ex- 
ternus). — The  external  pterygoid  arises  in  the  zygomatic 
fossa  by  two  heads,  an  upper  and  a  lower.  The  upper  head 
springs  from  the  infratemporal  ridge  and  the  zygomatic 
surface  of  the  great  wing  of  the  sphenoid ;  the  loiver  head 
takes  origin  from  the  outer  surface  of  the  external  pterygoid 
plate.  As  the  muscle  passes  backwards  it  diminishes  some- 
what in  width,  and  is  inserted  into  the  fore-part  of  the 
neck  of  the  mandible,  and  also  into  the  anterior  margin  of 
the  inter-articular  fibro- cartilage  of  the  temporo -maxillary 
articulation. 

Internal  Pterygoid  Muscle  (musculus  pterygoideus  in- 
ternus). — The  internal  pterygoid  is  also  bicipital  at  its  origin. 
Its  two  heads  embrace  the  origin  of  the  lower  head  of  the 
external  pterygoid.  The  superficial  and  smaller  head  of  the 
internal  pterygoid  springs  from  the  lower  and  back  part  of 
the  tuberosity  of  the  superior  maxilla  and  also  from  the  outer 
surface  of  the  tuberosity  of  the  palate  bone ;  the  deep  head. 
hidden  by  the  external  pterygoid,  arises  in  the  pterygoid 
fossa  from  the  inner  surface  of  the  external  pterygoid  plate, 
and  from  the  surface  of  the  tuberosity  of  the  palate  bone, 
which  appears  between  the  two  pterygoid  plates.  The  two 
heads  of  the  muscle  unite  at  the  lower  margin  of  the  fore- 
part of  the  external  pterygoid,  and  its  fibres  proceed  down- 
wards with  an  inclination  backwards  and  outwards.  They 
gain  insertion  into  the  angle  of  the  lower  jaw,  and  into  the 
lower  and  back  part  of  the  inner  aspect  of  the  ascending 
ramus  as  high  as  the  mandibular  foramen. 

Internal  Maxillary  Artery  (arteria  maxillaris  interna). — 
This  vessel  is  the  larger  of  the  two  terminal  branches  of  the 
external  carotid  artery,  and  takes  origin  within  the  substance 
of  the  parotid  gland,  immediately  behind  the  neck  of  the 
mandible.  From  this  it  proceeds  forwards  to  the  fore-part  of 
the  zygomatic  fossa,  where  it  disappears  from  view,  by  dipping 
between  the  two  heads  of  origin  of  the  external  pterygoid 
muscle,  and  entering  the  spheno- maxillary  fossa.  It  is 
customary  to  divide  it  into  three  parts  for  convenience  in 
description.  The  first  part  runs  horizontally  forwards  under 
cover  of  the  neck  of  the  mandible,  and  upon  the  internal 
lateral  ligament.  It  lies  along  the  lower  border  of  the 
posterior  part  of  the  external  pterygoid  muscle,  and  usually 
crosses  the  inferior  dental   nerve.      The  second  part  extends 


TEMPORAL  AND  PTERYGOID  REGIONS     285 

obliquely  upwards  and  forwards  upon  the  surface  of  the 
external  pterygoid  muscle,  and  under  cover  of  the  insertion 
of  the  temporal  muscle  into  the  coronoid  process  of  the 
mandible.  The  third  part  dips  between  the  two  heads  of  the 
external  pterygoid,  and  is  contained  in  the  spheno-maxillary 
fossa. 

Whilst  this  is  the  most  frequent  arrangement,  it  is  by  no 
means  uncommon  to  find  the  second  part  of  the  artery  lying 
in  a  deeper  plane,  viz.,  between  the  internal  and  external 
pterygoid  muscles.  In  this  case  the  vessel  makes  a  bend 
outwards  between  the  heads  of  the  external  pterygoid  muscle, 
and  appears  on  its  surface  before  entering  the  spheno- 
maxillary fossa. 

The  branches  of  the  internal  maxillary  artery  are  classified 
into  three  groups  according  to  the  portion  of  the  vessel  from 
which  they  spring.  One  branch  only  of  the  third  part,  viz., 
the  posterior  dental  or  the  superior  posterior  alveolar  artery,  can 
be  studied  in  this  dissection.  Those  arising  from  the  first 
and  second  parts  are  : — 


From  the  First  Part. 

From  the  Second  Part. 

1.  The  deep  auricular. 

2.  Tympanic. 

3.  Middle  meningeal. 

4.  Small  meningeal. 

5.  Inferior  dental. 

1.  Masseteric. 

2.  Pterygoid. 

3.  Anterior   and    posterior    deep 

temporal. 

4.  Buccal. 

The  deep  auricular  artery  (arteria  auricularis  profunda)  is  a 
small  vessel  which  pierces  the  anterior  wall  of  the  external 
auditory  meatus  to  supply  the  skin  which  lines  it,  and  also 
the  superficial  part  of  the  tympanic  membrane. 

The  meningeal  and  ty?npanic  branches  proceed  upwards 
under  cover  of  the  external  pterygoid  muscle,  and  therefore 
cannot  be  fully  studied  until  this  muscle  is  reflected. 

The  inferior  dental  artery  (arteria  alveolaris  inferior)  arises 
opposite  the  middle  meningeal,  and  runs  downwards  upon 
the  internal  lateral  ligament  to  enter  the  mandibular  foramen 
of  the  lower  jaw.  It  is  generally  accompanied  by  two  venae 
comites,  which  lie  one  upon  either  side  of  it,  and  it  is  placed 
behind  the  inferior  dental  nerve.  Just  before  entering  the 
canal,   the  inferior  dental  artery  gives  off  the  slender  mylo- 


286  HEAD  AND   NECK 

hyoid  branchy  which  is  carried  downwards  and  forwards  with 
the  corresponding  nerve,  upon  the  deep  aspect  of  the 
mandible,  to  the  digastric  triangle  of  the  neck. 

The  branches  from  the  second  part  are  given  off  for  the 
supply  of  the  neighbouring  muscles.  The  masseteric  (arteria 
masseterica)  passes  outwards  behind  the  temporal  muscle 
with  the  nerve  of  the  same  name,  and  has  been  seen 
entering  the  masseter  muscle.  The  pterygoid  branches  (rami 
pterygoidei)  are  a  few  irregular  twigs,  which  are  given  to 
the  pterygoid  muscles.  The  deep  temporal  arteries  (arteriae 
temporales  profundae)  are  two  in  number  —  anterior  and 
posterior — and  pass  upwards  in  the  fore  and  hinder  part  of 
the  temporal  fossa,  between  the  bony  wall  of  the  cranium 
and  the  temporal  muscle.  They  end  in  twigs  for  the  supply 
of  the  temporal  muscle,  and  anastomose  with  the  middle 
temporal  artery.  The  buccal  artery  (arteria  buccinatoria) 
accompanies  the  long  buccal  nerve,  and  is  distributed  to  the 
buccinator  muscle  and  the  mucous  membrane  of  the  cheek. 
It  anastomoses  with  the  facial  artery. 

The  posterior  superior  dental  bratich  (arteria  alveolaris 
superior  posterior),  from  the  third  part  of  the  internal 
maxillary  artery,  descends  upon  the  posterior  aspect  of  the 
superior  maxilla,  and  sends  branches  through  the  posterior 
dental  foramina  for  the  supply  of  the  upper  molar  and 
bicuspid  teeth  (Fig.  108).  Some  small  twigs  also  go  to  the 
gum,  whilst  others  find  their  way  to  the  lining  membrane  of 
the  antrum  of  Highmore. 

Pterygoid  and  Internal  Maxillary  Veins. — The  veins  in 
this  region  are  very  numerous,  but  they  cannot  be  studied 
satisfactorily  in  an  ordinary  dissection.  They  are  well  seen, 
however,  when  injected,  in  horizontal  sections  of  the  frozen 
head  made  at  the  level  of  the  external  pterygoid  muscle. 
They  constitute  a  dense  plexus,  termed  the  pterygoid  plexus, 
around  the  external  pterygoid  muscle.  Tributaries  corre- 
sponding to  the  branches  of  the  internal  maxillary  artery 
open  into  this  network,  whilst  the  blood  is  led  away  from  its 
back  part  by  a  short  wide  trunk,  called  the  internal  maxillary 
vein.  This  vessel  accompanies  the  first  part  of  the  internal 
maxillary  artery  into  the  parotid  gland,  and  joins  the  super- 
ficial temporal  vein  behind  the  neck  of  the  jaw,  to  form  the 
temporo-77iaxillary  trunk. 

The   pterygoid  venous  plexus  also  establishes,  by  various 


TEMPORAL  AND  PTERYGOID   REGIONS      287 

offsets,  certain  highly  important  connexions.  From  its  fore- 
part the  deep  facial  vein  proceeds  ;  this  extends  forwards  under 
cover  of  the  lower  jaw  and  the  masseter,  and  unites  with  the 
facial  vein.  Entering  its  upper  part  are  one  or  more  minute 
emissary  veins  from  the  cavernous  sinus.  These  gain  the 
exterior  of  the  cranium  by  passing  through  the  foramen  ovale. 
It  likewise  communicates  with  the  ophthalmic  vein  through 
the  spheno-maxillary  fissure. 

Temporo-Maxillary  Articulation  (articulatio  mandibularis) 
— This  joint  must  next  be  studied,  in  order  that  the  external 
pterygoid  muscle  may  be  thrown  forwards.  In  connexion 
with  it  we  find  : — 


Ligaments  Proper. 


1.  The  external  lateral. 

2.  The  capsular. 


Accessory  Ligaments. 


An  interarticular  fihro-cartilage. 


1.  Internal  lateral. 

2.  Stylo-maxillary. 


The  external  lateral  ligament  is  a  strong  band  which  is 
attached  above  to  the  outer  surface  of  the  posterior  part  of 
the  zygomatic  arch  and  to  the  tubercle  at  the  root  of  the 
zygoma.  It  is  composed  of  short  parallel  fibres,  which  pro- 
ceed obliquely  downwards  and  backwards  to  be  inserted  into 
the  outer  and  hinder  part  of  the  neck  of  the  lower  jaw. 

The  capsule  of  the  joint  consists  of  a  few  scattered  fibres, 
which  support  the  synovial  membranes  upon  the  inner, 
anterior,  and  posterior  aspects  of  the  articulation. 

The  internal  lateral  ligament  is  a  long  membranous  band 
which  springs  from  the  spinous  process  of  the  sphenoid  bone, 
and  is  attached  below  to  the  lingula  and  to  the  sharp  inner 
margin  of  the  mandibular  foramen  of  the  lower  jaw.  It  is  not 
in  direct  relationship  with  the  joint.  Above,  it  lies  under 
cover  of  the  external  pterygoid  muscle ;  lower  down,  the 
internal  maxillary  artery  intervenes  between  it  and  the  neck 
of  the  mandible ;  whilst,  still  lower,  the  inferior  dental  vessels 
and  nerve  are  interposed  between  it  and  the  ramus  of  the 
mandible. 

The  stylo-maxillary  ligament  has  already  been  noticed.  It 
is  an  aponeurotic  band,  derived  from  the  deep  cervical  fascia 
as  it  forms  a  part  of  the  capsule  of  the  parotid  gland.     It  is 


HEAD   AND   NECK 


attached  on  the  one  hand  to  the  styloid  process,  and  on  the 
other  to  the  angle  and  posterior  border  of  the  ramus  of  the 
jaw  between  the  internal  pterygoid  and  masseter  muscles. 

An  examination  of  these  ligaments  will  show  that  very 
little  is  added  to  the  strength  of  the  joint  by  their  presence. 
The  security  of  the  joint  depends  not  so  much  upon  its  liga- 
ments as  upon  the  strong  muscles  of  mastication,  which  keep 
the  head  of  the  mandible  in  its  place. 

The  interarticular  fibro-cartilage  is  an  oval  plate,  with  its 
long  axis  directed  transversely.  It  is  interposed  between  the 
condyle  of  the  mandible  and  the  glenoid  cavity,  and  divides 
the  joint  cavity   into   an   upper  and  lower  portion,   each  of 


Eminentia  articularis 


Upper  joint  cavity 
Meniscus 
Lower  joint  cavity 
Capsule 


/ 
Mastoid  process 

Styloid 


MANDIBl 


Fig.   109. — Section  through  Temporo-maxillary  Joint. 

which  is  provided  with  a  separate  synovial  membrane.  To 
expose  the  cartilage,  the  external  lateral  ligament  must  be 
removed.  It  will  then  be  seen  to  be  adapted  to  the  two 
bony  surfaces  between  which  it  lies.  Above,  it  is  concavo- 
convex  in  correspondence  with  the  eminentia  articularis  and 
the  glenoid  fossa  of  the  temporal  bone ;  whilst  below,  it  is 
concave,  and  fits  upon  the  upper  aspect  of  the  condyle  of  the 
mandible.  In  the  centre  it  is  thin,  and  in  some  cases  may 
be  seen  to  be  perforated.  Its  circumference,  more  especially 
posteriorly,  is  thick.  It  should  also  be  noted  that  it  is  but 
loosely  attached  by  its  periphery  to  the  external  lateral  liga- 
ment, and  that  anteriorly  the  external  pterygoid  muscle  is 
partly  inserted  into  it. 

The  synovial  membrane  which  lines  the  upper  cavity  of  the 


TEMPORAL  AND  PTERYGOID  REGIONS      289 


joint  is  of  greater  extent  and  looser  than  that  which  lines 
the  lower  compartment.  This  is  owing  to  the  articular 
surface  of  the  temporal  bone  being  of  larger  size  than  the 
condylar  surface. 

Movements.  —  The  movements  which  the  mandible  can  perform  at 
the  temporo- maxillary  joint  are  the  following:  —  (1)  depression;  (2) 
elevation  ;  (3)  protraction  ;  (4)  retraction  ;  (5)  lateral  or  chewing  move- 
ments. When  the  lower  jaw  is  depressed  the  interarticular  fibro-cartilage 
with  the  condyle  of  the  mandible  moves  forwards  in  the  glenoid  fossa, 
and  the  latter  finally  takes  up  a  position  on  the  eminentia  articularis. 
This  forward  gliding  of  cartilage  and  condyle  in  the  upper  compartment 
of  the  joint  is  accompanied  by  another  movement  in  the  lower  compart- 
ment of  the  joint,  which  consists  in  a  rotation  of  the  condyle  of  the 
mandible  on  the  lower  surface  of 
the  interarticular  fibro  -  cartilage. 
Elevation  of  the  mandible  or  closure 
of  the  mouth  is  brought  about  by  a 
reverse  series  of  changes  in  both 
compartments  of  the  joint.  Whilst 
these  movements  are  going  on,  the 
mandible  rotates  around  a  trans- 
verse axis  which  traverses  the  bone 
in  the  neighbourhood  of  the  mandi- 
bular foramen.  This  is  the  point, 
therefore,  of  least  movement,  and 
consequently  in  opening  and  shut- 
ting the  mouth  the  inferior  dental 
vessels  and  nerves  are  not  unduly 
stretched.  In  protraction  and  re- 
traction the  movement  is  chiefly 
confined  to  the  upper  compartment 
of  the  joint.  The  condyle  of  the 
mandible  with  the  interarticular 
fibro-cartilage  glides  forwards  and 
backwards      upon     the     temporal 

articular  surface.  In  the  lateral  movements  of  the  jaw  the  mandible  is 
carried  alternately  from  side  to  side,  as  in  the  process  of  chewing. 

The  muscles  on  each  side  which  are  chiefly  engaged  in  producing  these 
movements  are  the  following: — (1)  depressors — the  platysma,  the  mylo- 
hyoid, and  the  anterior  belly  of  the  digastric  ;  (2)  elevators — the  masseter, 
internal  pterygoid,  temporal;  (3)  protractors — the  external  pterygoid,  and 
to  some  extent  the  internal  pterygoid  and  the  superficial  fibres  of  the 
masseter;  (4)  retractor — the  posterior  fibres  of  the  temporal;  (5)  lateral 
movement  is  produced  by  certain  of  the  muscles  of  opposite  sides  acting 
alternately. 


Fig.  no. — Diagram  of  the  different 
positions  occupied  by  the  head  of  the 
mandible  and  the  interarticular  carti- 
lage as  the  mouth  is  opened  and  closed. 


Reflection  of  External  Pterygoid. — The  hea/1  of  the  lower  jaw  should 
now  be  disarticulated  and  thrown  forwards  with  the  attached  external 
pterygoid  muscle.  It  is  well  to  detach  the  interarticular  fibro-cartilage 
with  the  head  of  the  bone,  in  order  that  it  may  be  more  thoroughly  ex- 
amined. Care  must  be  taken  not  to  injure  the  auriculotemporal  nerve, 
which  passes  backwards  in  close  proximity  to  the  deep  aspect  of  the  joint. 
When  the  disarticulation  is  complete,  the  muscle  may  be  turned  forwards 

VOL.   II  — 19 


29o  HEAD   AND   NECK 

by  gently  insinuating  the  head  of  the  jaw  under  the  internal  maxillary 
artery. 

The  reflection  of  the  external  pterygoid  muscle  brings  into  view,  after 
a  little  dissection,  the  inframaxillary  division  of  the  trigeminal  nerve, 
emerging  from  the  foramen  ovale,  and  breaking  up  into  its  branches  of 
distribution.  The  slender  chorda  tympani  will  likewise  be  found  proceeding 
downwards  and  forwards  to  join  the  lingual  nerve,  and  the  middle  menin- 
geal, tympanic,  and  small  meningeal  arteries  may  be  traced  to  the  points 
where  they  leave  the  space. 

Middle  and  Small  Meningeal  and  Tympanic  Arteries. — 

The  middle  meningeal  artery  (arteria  meningea  media)  has 
already  been  seen  arising  from  the  first  part  of  the  internal 
maxillary  artery.  It  proceeds  upwards  under  cover  of  the 
external  pterygoid  muscle,  and  disappears  from  view  by 
entering  the  foramen  spinosum,  and  thus  gaining  the  cranial 
cavity  (p.  130).  It  will  generally  be  observed  to  be  embraced 
by  the  two  heads  of  origin  of  the  auriculo-temporal  nerve. 

The  small  meningeal  (ramus  meningeus  accessorius)  and 
ty77ipa?iic  (arteria  tympanica)  arteries  arise  more  frequently 
from  the  preceding  vessel  than  from  the  trunk  of  the  internal 
maxillary.  The  small  meningeal  inclines  forwards  and  up- 
wards, and  enters  the  cranial  cavity  by  passing  through  the 
foramen  ovale ;  the  tympanic  runs  upwards  and  slightly  back- 
wards, and  reaches  the  tympanum  by  passing  through  the 
Glaserian  fissure.  In  the  tympanic  cavity  it  anastomoses  with 
the  stylo-mastoid  branch  of  the  posterior  auricular  artery. 

Inferior  Maxillary  Division  of  the  Trigeminal  Nerve 
(nervus  mandibularis). — The  inferior  maxillary  nerve  arises 
within  the  cranium  from  the  Gasserian  ganglion,  and  enters 
the  pterygo-maxillary  region  through  the  foramen  ovale.  It 
is  composed  of  sensory  fibres,  but  it  is  accompanied  through 
the  foramen  by  the  small  motor  root  of  the  trigeminal  nerve, 
and,  a  junction  being  effected  between  the  two  immediately 
after  they  gain  the  exterior  of  the  cranium,  a  mixed  nerve-trunk 
is  the  result.  This  nerve-trunk  lies  under  cover  of  the  ex- 
ternal pterygoid  muscle,  and  after  a  very  short  course  (not 
exceeding  two  or  three  lines)  it  ends  by  dividing  into  two 
parts,  named  the  anterior  and  posterior  divisions  of  the  inferior 
maxillary  nerve  (Fig.  in). 

Before  it  divides,  the  trunk  of  the  inferior  maxillary  nerve 
gives  off  two  branches,  viz.,  (1)  the  recurrent  nerve  (nervus 
spinosus),  and  (2)  the  nerve  to  the  internal  pterygoid  muscle. 

The  recurrent  nerve  is  a  very  slender  twig  which  enters 


TEMPORAL  AND  PTERYGOID  REGIONS     291 

the  cranium  by  accompanying  the  middle  meningeal  artery 
through  the  foramen  spinosum  to  supply  the  dura  mater. 

The  internal  pterygoid  nerve  will  be  found  passing  under 
cover  of  the  posterior  border  of  the  internal  pterygoid 
muscle  close  to  its  origin.  In  close  relation  to  the  root  of 
this  nerve  is  the  otic  ganglion. 


GASSERIAN    GANGLION. 
ophthau:  DIV; 


FlG.  i  11. — Diagram  of  the  Gassenan  Ganglion  and  the  Inferior  Maxillary 
Division  of  the  Fifth  or  Trigeminal  Nerve.  The  motor  root  of  the 
fifth  nerve  is  tinted  yellow. 

From  the  two  terminal  divisions  of  the  inferior  maxillary 
trunk  the  chief  branches  of  distribution  arise.  The  anterior 
division  is  much  the  smaller  of  the  two,  and  is  composed  almost 
entirely  of  motor  fibres  derived  from  the  motor  root  of  the 
trigeminal  nerve.  The  only  sensory  fibres  which  it  contains 
are  chose  which  form  the  long  buccal  nerve.  It  gives  off  the 
following  branches: — 


1.  Masseteric. 

2.  Two  deep  temporal. 


External  pterygoid. 

Long  buccal. 


The  large  posterior  division  is  chiefly  sensory.      It  contains 
11 — 19  « 


292  HEAD  AND  NECK 

only  a  very  few  fibres  from  the  motor  root,  and  these  are 
prolonged  into  its  inferior  dental  branch,  and  afterwards 
come  off  in  the  form  of  the  mylo-hyoid  nerve.  The  branches 
of  the  posterior  division  are  : — 

i.   Auriculotemporal. 

2.  Inferior  dental. 

3.  Lingual  (or  gustatory). 

The  masseteric  ?ierve  (nervus  massetericus)  is  directed 
outwards  above  the  external  pterygoid  muscle,  and,  passing 
through  the  sigmoid  notch  behind  the  posterior  border  of 
the  temporal  muscle,  it  enters  the  hinder  and  upper  part 
of  the  deep  surface  of  the  masseter.  In  the  substance  of 
this  muscle  it  may  be  traced  with  the  companion  artery 
downwards  and  forwards  to  its  lower  and  fore  part.  Before 
reaching  the  masseter,  it  gives  one  or  two  twigs  to  the 
temporo-maxillary  joint. 

The  deep  temporal  nerves  (nervi  temporales  profundi)  are 
usually  two  in  number,  and  are  termed  anterior  and  posterior 
according  to  the  position  they  occupy  in  the  temporal  fossa. 
The  posterior  nerve  is  the  smaller  of  the  two,  and  frequently 
arises  by  a  common  root  with  the  masseteric.  Both  deep 
temporal  nerves  pass  outwards  above  the  external  pterygoid, 
and  then  turn  upwards  upon  the  bony  wall  of  the  cranium. 
After  a  short  course  they  end  in  twigs  which  penetrate  the 
substance  of  the  temporal  muscle. 

Long  Buccal  Nerve  (nervus  buccinatorius). — The  long 
buccal  is  the  largest  of  the  branches  proceeding  from  the 
anterior  division  of  the  inferior  maxillary  nerve.  It  proceeds 
outwards  between  the  two  heads  of  the  external  pterygoid 
muscle,  and  then  runs  downwards  and  forwards  under 
cover  of  the  temporal  muscle,  and  also  of  the  anterior 
border  of  the  masseter,  to  reach  the  outer  surface  of  the 
buccinator  muscle.  Here  it  has  been  seen  to  form  with 
branches  of  the  facial  nerve  the  buccal  plexus,  and  to  be 
distributed  to  the  mucous  membrane  and  skin  of  the 
cheek  (p.  266). 

The  long  buccal  is  a  sensory  nerve,  and  all  the  sensory 
fibres  in  the  anterior  division  of  the  inferior  maxillary  nerve 
enter  into  its  composition.  A  few  motor  fibres,  however, 
are  also  prolonged  into  it ;  these  come  off  from  it  in  two 
branches,    viz.,    (1)    in    the    nerve   to    the    external  pterygoid, 


TEMPORAL  AND  PTERYGOID  REGIONS     293 

which  as  a  rule  arises  in  common  with  the  long  buccal 
and  at  once  sinks  into  the  deep  surface  of  this  muscle ;  and 
(2)  in  a  third  twig  of  supply  to  the  temporal  muscle.  This 
temporal  branch  springs  from  the  long  buccal  after  it  has 
reached  the  outer  surface  of  the  external  pterygoid,  and 
proceeds  upwards  to  supply  the  fore-part  of  the  temporal 
muscle  (Fig.  108).  In  some  cases  the  long  buccal  nerve 
may  be  observed  to  pierce  the  temporal  muscle  instead  of 
passing  under  cover  of  it. 

Auriculo-Temporal  Nerve  (nervus  auriculo-temporalis). — 
The  auriculotemporal,  composed  of  sensory  fibres,  springs 
from  the  posterior  division  of  the  inferior  maxillary  by  two 
roots.  These  pass  backwards  under  cover  of  the  external 
pterygoid  muscle  and  embrace  the  middle  meningeal  artery. 
Beyond  this  vessel  they  unite,  and  the  nerve  is  continued 
backwards  between  the  neck  of  the  lower  jaw  and  the 
internal  lateral  ligament.  Gaining  the  interval  between  the 
ear  and  jaw,  it  turns  upwards  in  relation  to  the  deep  surface 
of  the  parotid  gland,  and  crosses  the  zygoma  in  company 
with  the  superficial  temporal  artery.  Its  further  course  has 
already  been  examined  (p.  no). 

The  following  branches  proceed  from  it: — (1)  one  or  two 
strong  branches  of  communication  to  the  temporo-facial 
nerve;  (2)  a  few  slender  filaments  which  enter  the  posterior 
aspect  of  the  temporo-maxillary  joint;  (3)  some  twigs  to  the 
parotid  gland ;  (4)  terminal  filaments  to  the  skin  over  the 
temporal  region  and  summit  of  the  head  (p.  no);  (5)  auri- 
cular branches. 

The  auricular  branches  are  usually  two  to  the  skin  lining 
the  interior  of  the  external  auditory  meatus,  and  two  to  the 
integument  over  the  upper  and  fore  part  of  the  pinna.  The 
former  gain  the  interior  of  the  meatus  by  passing  between 
the  osseous  and  cartilaginous  portions  of  the  canal. 

Inferior  Dental  Nerve  (nervus  alveolaris  inferior). — This 
is  the  largest  branch  of  the  inferior  maxillary.  Emerging 
from  under  cover  of  the  external  pterygoid  muscle,  it 
passes  downwards  upon  the  internal  lateral  ligament  of 
the  lower  jaw  and  enters  the  mandibular  foramen.  The 
inferior  dental  artery  runs  downwards  behind  it,  whilst 
the  lingual  nerve  is  in  front  of  it  and  upon  a  somewhat 
deeper  plane.  The  inferior  dental  is  a  sensory  nerve,  but 
a    few    motor    fibres    from    the     motor    root    are    prolonged 

u—196 


294  HEAD  AND  NECK 

downwards  within  its  sheath  as  far  as  the  mandibular 
foramen.  At  this  point  they  come  off  as  the  slender 
mylo-hyoid  7ierve. 

The  mylo-hyoid  nerve,  accompanied  by  the  artery  of  the 
same  name,  pierces  the  internal  lateral  ligament  and  pro- 
ceeds downwards  and  forwards  in  a  groove  upon  the  deep 
surface  of  the  lower  jaw  to  the  digastric  triangle.  A 
narrow  prolongation  of  the  internal  lateral  ligament  bridges 
over  the  groove  and  holds  the  nerve  and  vessel  in  position. 
In  the  digastric  triangle  the  mylo-hyoid  nerve  has  already 
been  dissected.  It  appears  upon  the  surface  of  the  mylo- 
hyoid muscle,  and,  issuing  from  under  cover  of  the  super- 
ficial part  of  the  submaxillary  gland,  it  breaks  up  into 
numerous  branches  for  the  supply  of  two  muscles,  viz.,  (i) 
the  mylo-hyoid,  and  (2)  the  anterior  belly  of  the  digastric. 

Lingual  Nerve. — This  nerve  is  entirely  sensory,  and  is 
covered  in  the  first  part  of  its  course,  like  the  other  branches 
of  the  inframaxillary  nerve,  by  the  external  pterygoid  muscle. 
Appearing  at  the  lower  border  of  this  muscle,  it  proceeds 
downwards  and  forwards  between  the  internal  pterygoid 
muscle  and  the  mandible  and  enters  the  submaxillary  region, 
where  it  will  afterwards  be  traced  to  the  tongue.  It  is  placed 
in  front  of  and  on  a  slightly  deeper  plane  than  the  inferior 
dental  nerve.  In  this  region  it  gives  off  no  branches,  but, 
under  cover  of  the  external  pterygoid,  it  is  joined  at  an  acute 
angle  by  the  chorda  tympani  branch  of  the  facial  nerve.  Not 
infrequently,  also,  a  communicating  twig  passes  between  it 
and  the  inferior  dental  nerve. 

Chorda  Tympani. — This  is  a  slender  nerve  which  arises 
from  the  facial  in  the  aqueduct  of  Fallopius.  It  gains  the 
pterygo- maxillary  region  by  traversing  the  tympanic  cavity 
and  appearing  through  the  inner  part  of  the  Glaserian  fissure. 
It  will  now  be  seen  to  run  downwards  and  forwards  under 
cover  of  the  internal  lateral  ligament  of  the  lower  jaw,  and 
unite  with  the  lingual  nerve  near  its  origin.  It  is  joined  by  a 
slender  filament  from  the  otic  ganglion. 

Otic  Ganglion. — As  this  ganglion  lies  under  cover  of  the 
inferior  maxillary  trunk,  it  cannot  be  satisfactorily  studied  at 
this  stage.  It  is  true  that  it  may  be  exposed  by  tracing  the 
nerve  to  the  internal  pterygoid  muscle  upwards,  when  it  will 
be  seen  to  be  developed  in  connexion  with  the  root  of  this 
branch.      Its  connexions,  however,  can  only  be  made  out  by 


TEMPORAL  AND  PTERYGOID   REGIONS      295 

dissecting  from  the  inside,  and  it  is  well  to  defer  its  examina- 
tion until  this  can  be  done. 

Dissection. — The  student  should  now  endeavour,  by  means  of  a  Hey's 
saw,  a  chisel,  and  the  bone  pliers,  to  remove  the  outer  table  of  the  lower 
jaw,  and  thus  open  up  the  mandibular  canal. 

Structures  within  the  Mandibular  Canal. — This  canal  is 
traversed  by  the  inferior  dental  vessels  and  nerve.  These  give 
off  twigs  which  enter  the  fangs  of  the  molar  and  bicuspid 
teeth,  and  each  terminates  by  dividing  into  a  mental  and 
incisor  branch. 

The  mental  artery  and  nerve  appear  on  the  face  through 
the  mental  foramen,  and  have  already  been  examined ;  the 
incisor  artery  and  nerve  are  carried  forwards  to  the  symphysis 
and  send  up  twigs  to  the  canine  and  incisor  teeth.  The 
vessel  anastomoses  in  the  bone  with  the  corresponding  artery 
of  the  opposite  side. 


SUBMAXILLARY  REGION. 

The  superficial  area  of  the  submaxillary  region  has  already 
been  dissected,  under  the  name  of  the  anterior  part  of  the 
digastric  or  submaxillary  triangle  (p.  204).  It  is  now  necessary 
to  carry  the  dissection  to  a  deeper  plane,  in  order  to  expose 
a  number  of  parts  in  connexion  with  the  tongue  and  floor  of 
the  mouth.     The  structures  thus  displayed  are  : — 

1.  Mylo-hyoid  muscle. 

2.  Submaxillary  gland  and  its  duct. 

3.  Sublingual  gland. 

4.  Side  of  the  tongue,  and  the  mucous  membrane  of  the  mouth. 

f  Hyoglossus. 

5.  Muscles.     J  Styloglossus. 
3  J   Geniohyoid. 

V.  Genio-hyoglossus. 

(   Hypoglossal. 

6.  Nerves.       -J    Lingual. 

^   Glosso- pharyngeal. 

7.  Submaxillary  ganglion. 

8.  Lingual  artery  and  veins. 

9.  Stylo-hyoid  ligament. 

Dissection. — To  prepare  the  part  for  dissection,  it  is  necessary  to  throw 
back  the  head  to  its  full  extent,  and  turn  it  slightly  to  the  opposite  side. 
If  the  stuffing  in  the  mouth  has  not  been  previously  removed  in  the 
dissection  of  the  pterygo-maxillary  region,  it  should  be  taken  out  now,  and 


296  HEAD  AND  NECK 

then  the  tip  of  the  tongue  should  be  seized  with  the  forceps,  and  drawn 
forcibly  forwards  between  the  teeth,  and  retained  in  this  position  by 
stitching  it  to  the  nose. 

In  dissecting  towards  the  mesial  plane,  three  muscular  strata  are 
encountered,  viz.,  the  mylohyoid,  the  hyoglossus,  the  genio-hyoglossus. 
In  the  intervals  between  these,  certain  important  structures  will  be  exposed. 
Begin  with  the  first  muscular  stratum. 

The  mylo-hyoid  muscle  forms  the  fore-part  of  the  floor  of  the  digastric 
triangle.  To  bring  it  fully  into  view,  certain  of  the  contents  of  this  space 
must  be  displaced.  Divide  the  facial  artery  at  the  point  where  it  gains 
the  lower  jaw,  and,  disengaging  it  from  the  submaxillary  gland,  throw  it 
downwards,  along  with  its  submental  branch  and  the  facial  vein.  Next, 
detach  the  anterior  belly  of  the  digastric  from  the  mandible,  and  deal  with 
it  in  the  same  manner.  The  mylo-hyoid  nerve  must  also  be  cut,  and  the 
superficial  part  of  the  submaxillary  gland  turned  backwards.  The  super- 
ficial surface  of  the  mylo-hyoid  is  in  this  way  completely  exposed,  and  its 
fibres  may  be  cleaned  and  its  attachments  made  out. 

Mylo-hyoid  (musculus  mylohyoideus). — This  is  a  thin 
sheet  of  muscular  fibres,  which  arises  from  the  mylo-hyoid 
ridge  upon  the  deep  surface  of  the  body  of  the  mandible  by 
an  origin  which  extends  from  the  last  molar  tooth  behind  to 
the  symphysis  in  front.  Its  fibres  are  directed  downwards, 
inwards,  and  backwards,  and  present  two  different  modes  of 
insertion.  The  posterior  fibres  are  inserted  into  the  body  of 
the  hyoid  bone ;  these,  however,  form  a  comparatively  small 
part  of  the  muscle.  The  greater  number  of  the  fibres  are 
inserted  into  a  median  raphe,  which  extends  between  the 
symphysis  of  the  lower  jaw  and  the  body  of  the  hyoid  bone. 
The  two  mylo-hyoid  muscles,  therefore,  in  front  of  the  hyoid 
bone  stretch  across  from  one  side  of  the  body  of  the  mandible 
to  the  other,  and  constitute  a  floor  for  the  anterior  part  of  the 
mouth.  This  floor  is  frequently  termed  the  diaphragma  oris. 
The  mylo-hyoid  muscle  is  supplied  by  the  mylo-hyoid  branch 
of  the  inferior  dental  nerve. 

Dissection. — The  mylo-hyoid  muscle  must  now  be  reflected,  in  order 
that  the  parts  subjacent  to  it  may  be  brought  into  view.  As  these  parts 
lie  in  a  great  measure  under  shelter  of  the  mandible,  it  is  advantageous  to 
make  at  the  same  time  a  section  of  this  bone,  in  order  that  it  may  be  turned 
upwards. 

Carefully  divide  the  fibres  of  the  mylo-hyoid  muscle  close  to  the  ridge 
from  which  it  arises.  A  small  piece  may  be  left  attached  to  the  mandible 
to  serve  as  a  landmark  in  the  future  dissection.  This  must  be  done 
cautiously,  else  the  mucous  membrane  of  the  mouth  will  be  injured.  When 
detached  from  the  jaw,  the  muscle  must  next  be  separated  from  the  median 
raphe,  and  then  it  can  be  thrown  down  over  the  hyoid  bone.  The  lower 
jaw  should  next  be  divided,  by  means  of  the  saw  and  bone  pliers,  a 
quarter  of  an  inch  to  the  outer  side  of  the  symphysis.  When  the  section  is 
completed,  the  lower   margin    of  the    mandible    should    be   gently  tilted 


SUBMAXILLARY  REGION 


297 


upwards,  and  some  means  taken  to  retain  the  loose  piece  of  the  bone  in 
this  position.  Under  no  pretence  whatever  should  it  be  removed,  and  care 
must  be  taken  to  preserve  intact  the  mucous  membrane  passing  from  the 
floor  of  the  mouth  to  the  deep  surface  of  the  gum. 

Parts  Exposed  by  the  Reflection  of  the  Mylo-hyoid  (Fig. 
112). — The  side  of  the  tongue  is  now  brought  into  view, 
with  a  number  of  structures  in  connexion  with  it.  First 
note  the  mucous  membrane  stretching  from  the  tongue  to 
the  gum  of  the  lower  jaw ;  then  identify  the  various  muscles. 


Styloglossus 

Stylo-pharyngeus 
Glossopharyngeal 
nerve 

Stylo-hyoid 
ligament 

(Lingual  nerve 


Deep  part  of  submaxillary  gland 
Submaxillary  ganglion 
Whai  ton's  duct 

Cut  edge  of  mucous  membrane 
Sublingual  gland 
ai)^  Sublingual  artery 

Genio- 
hyoglossus 


nio-hyoid 


Lingual  artery 
Middle  constrictor 


Lingual  artery 


Hypoglossal  nerve 
■a-hyoid  artery 

Fig.  112. — Dissection  of  Submaxillary  Region. 


The  hyoglossus,  a  portion  of  which  was  previously  visible 
behind  the  mylo-hyoid,  is  fully  exposed.  It  is  a  quadrangular 
sheet  of  fleshy  fibres  which  extends  from  the  hyoid  bone  to 
the  side  of  the  tongue.  Mark  its  position,  because  all  the 
structures  in  this  region  have  a  more  or  less  intimate  relation- 
ship to  it.  Thus,  behind,  and  to  some  extent  superficial  to 
its  upper  part,  will  be  recognised  the  stylo-glossus  muscle,  whilst 
in  front  of  it  are  the  genio- hyoglossus  and  the  genio -hyoid. 
The  genio-hyoid  muscle  occupies  the  fore-part  of  the  region, 
whilst  the  anterior  part  of  the  genio-hyoglossus  is  seen  in  the 
interval  between  it  and  the  hyoglossus.      Upon  the  surface  of 


298 


HEAD  AND  NECK 


the  hyoglossus,  the  lingual  and  hypoglossal  nerves,  the  deep 
portion  of  the  submaxillary  gland  with  Wharton's  duct,  and 
the  submaxillary  ganglion  are  to  be  dissected.  The  lingual 
?ierve  occupies  the  highest  level,  and  passes  forward  upon  the 
muscle  near  its  insertion  into  the  tongue.  The  hypoglossal 
?ierve,  accompanied  by  the  ranine  veiti,  crosses  it  close  to  the 
hyoid  bone,  whilst  the  deep  part  of  the  submaxillary  gland 
and  Wharton's  duct  occupy  an  intermediate  place.      Although 


Internal  pterygoid 
External  pterygoid 


Inferior  turbinated  bone 
Soft  palate 


Temporal  muscle 


Stylo-glossus 

Inferior  dental 

vessels  and  nerve 

Lingual  nerve 

Facial  artery- 
Superficial  part  of   x 
submaxillary-  gland "^XWJW^ 
Wharton's  duct^V^^^* 
Deep  part  of>>^3 
submaxillary  gland      \x^ 
Hypoglossal  nerve 

Lingual  artery 

Hyoglossus 

Mylo-hyoid 
Digastric  tendon 
Genio-hy 


Tongue 

Inferior  dental 
vessels  and  nerve 
in  the  mandib- 
ular canal 
Facial  artery 


Mylo-hyoid 
Lingual  nerve 
'Deep  part  of 
submaxillary  gland 
'Wharton's  duct 
Hypoglossal  nerve 
Lingual  artery 
\        'Digastric 
Hyoglossus 


^Genio-hyoid 


Fig.   113. — Coronal  section  through  the  Tongue  and  Submaxillary  Region 
in  a  plane  behind  the  molar  teeth. 

the  submaxillary  ganglion  is  very  minute,  its  relations  are 
so  precise  that  it  is  very  easily  found.  By  seizing  hold  of 
the  lingual  nerve  and  dissecting  carefully  with  the  point  of 
the  knife  in  the  interval  between  it  and  the  deep  part  of  the 
submaxillary  gland,  the  ganglion  will  be  exposed  and  its  roots 
and  branches  of  distribution  made  out.  Upon  the  genio- 
hyoglossus,  in  front  of  the  hyoglossus  the  dissector  will  note 
the  sublingual  gland  with  its  artery  of  supply.  Certain 
structures  will  also  be  seen  passing  under  cover  of  the 
posterior   margin   of  the    hyoglossus    muscle ;   these   are : — 


SUBMAXILLARY  REGION 


299 


(1)  the  glossopharyngeal  nerve  immediately  below  the  stylo- 
glossus muscle;  (2)  the  stylo-hyoid  ligament,  a  little  lower 
down  ;  and  (3)  the  lingual  artery,  close  to  the  hyoid  bone. 

Hyoglossus. — This  is  a  quadrate  flat  muscle  which  arises 
from  the  whole  length  of  the  greater  cornu,  and  also  from 
the  body  of  the  hyoid  bone.  Its  fibres  pass  upwards  to  the 
posterior  part  of  the  side  of  the  tongue,  where  they  ascend 


Parotid  duct 


Lower  jaw 

Wharton's  d 
Mucous  membrane 
Sublingual 


Internal  pterygoid 


Lingual  nerve 

Lower  jaw 
Mylo-hyoid 
Surface  of  submaxil- 
lary gland  covered 
by  mandible 
urface  covered  by 
tegument  and  fasciae 


Mylo-hyoid' 
Anterior  belly  of  digastric' 

FlG.    i  14.  —Dissection  of  the  Parotid,  Submaxillary,  and  Sublingual  Glands. 

under  cover  of  the  stylo-glossus.     The  hyoglossus  is  supplied 
by  the  hypoglossal  nerve. 

Styloglossus. — The  stylo-glossus  muscle  is  an  elongated 
fleshy  slip  which  takes  origin  from  the  anterior  aspect  of  the 
styloid  process  near  its  tip  and  also  to  a  slight  extent  from 
the  upper  end  of  the  stylo-hyoid  ligament.  Passing  down- 
wards and  forwards,  its  fibres  may  be  traced  upon  the  side 
of  the  tongue  as  far  as  the  tip.  They  decussate  with  the 
fasciculi  of  the  hyoglossus  muscle.  The  nerve  of  supply  to 
the  stylo-glossus  comes  from  the  hypoglossal. 


3°° 


HEAD  AND  NECK 


Genio-hyoid  (musculus  geniohyoideus). — The  genio-hyoid 
muscle  is  placed  close  to  the  mesial  plane,  in  contact  with  its 
fellow  of  the  opposite  side.  It  is  a  short  muscle  which  arises 
from  the  lower  of  the  two  genial  tubercles  upon  the  posterior 
surface  of  the  symphysis  of  the  mandible,  and  extends  down- 
wards and  backwards  to  gain  insertion  into  the  fore  aspect  of 
the  body  of  the  hyoid  bone.  The  hypoglossal  gives  the  nerve 
of  supply  to  the  genio-hyoid. 


Inferior  meatus  of  nose 


Tongue 


Vestibule  of 
mouth 


Sublingual  gland 
Wharton's  duct- 
Lingual  nerve 


Genio-hyoglossu 


\ntrum  of  Highmore 


Great  posterior 
.palatine  artery 
and  nerve 
Vestibule  of 
mouth 


Buccinator 


Ranine  artery 


Sublingual  gland 

Inferior  dental 
artery  and  nerve 
in  the  mandibular 
canal 
~Mylo-hyoid 

Platysma 


Genio-hyoid  Anterior  belly  of  digastric 

Fig.   115. — Coronal  section  through  the  Closed  Mouth  in  the  plane 
of  the  second  molar  teeth. 

Submaxillary  Gland  (glandula  submaxillaris). — The  sub- 
maxillary gland  consists  of  a  superficial  and  a  deep  portion  ; 
the  superficial  or  itiain  part  has  already  been  noted  as  the 
most  conspicuous  object  in  the  digastric  triangle.  In  size 
and  shape  it  may  be  compared  to  a  walnut,  and  it  is  contained 
within  a  capsule  derived  from  the  deep  cervical  fascia.  Its 
superficial  surface  presents  two  areas,  an  upper  and  a  lower. 
Of  these  the  upper  lies  under  shelter  of  the  body  of  the  lower 
jaw  and  looks  upwards  and  outwards ;  the  lower,  which  looks 
downwards  and  outwards,  is  covered  by  the  skin,  superficial 
fascia,  platysma,  deep  fascia,  and  is  crossed  by  the  facial 
vein.     The  deep  surface  of  the  gland  rests  upon  the  mylo-hyoid, 


SUBMAXILLARY  REGION  301 

and  behind  this  upon  the  hyoglossus  and  the  posterior  belly 
of  the  digastric  with  the  stylo-hyoid.  From  this  surface  the 
deep  part  of  the  gland  is  prolonged  forwards  under  cover  of 
the  mylo-hyoid  muscle  along  with  the  duct.  Lodged  in  a 
deep  groove  upon  the  posterior  and  upper  aspects  of  the 
gland  is  the  facial  artery  (Fig.  113). 

Wharton's  Duct  (ductus  submaxillaris). — The  duct  of  the 
submaxillary  gland  is  termed  IVharton's  duct.  It  emerges  from 
the  deep  surface  of  the  main  part  of  the  gland,  and  with  the 
deep  part  of  the  gland  it  proceeds  forwards  upon  the  hyo- 
glossus muscle  between  the  lingual  nerve  which  lies  above  it 
and  the  hypoglossal  nerve  which  is  placed  below  it.  Reaching 
the  surface  of  the  genio-hyoglossus  muscle,  it  inclines  slightly 
upwards  and  is  crossed  by  the  lingual  nerve.  Here  it  passes 
under  cover  of  the  sublingual  gland,  and  gains  the  floor  of 
the  mouth,  where  it  opens  by  a  small  orifice  placed  on  the 
summit  of  a  papilla  which  lies  close  to  the  side  of  the  frenum 
linguae. 

The  wall  of  Wharton's  duct  is  much  thinner  than  that  of 
the  parotid  duct.  If  a  small  opening  be  made  in  it,  the 
dissector  will  experience  little  difficulty  in  passing  a  fine  probe 
or  bristle  along  it  into  the  mouth. 

Sublingual  Gland  (glandula  sublingualis). — The  sublingual 
gland  lies  on  the  floor  of  the  mouth,  and  is  the  smallest  of 
the  three  salivary  glands.  It  has  an  elongated  shape,  and  in 
length  it  measures  about  one  inch  and  a  half.  Its  relations 
are  very  definite.  Its  prominent  upper  border  can  be  seen 
within  the  mouth,  beneath  the  fore-part  of  the  tongue,  where 
it  is  covered  by  a  fold  of  mucous  membrane  termed  the  plica 
sublingualis  (Fig.  115).  Internally  it  rests  upon  the  genio- 
hyoglossus  muscle,  whilst  externally  it  is  lodged  in  a  fossa  on 
the  deep  aspect  of  the  mandible,  immediately  external  to  the 
symphysis,  and  above  the  mylo-hyoid  ridge.  Below,  it  is 
supported  by  the  mylo-hyoid  muscle.  Its  anterior  extremity 
reaches  the  mesial  plane  above  the  anterior  border  of  the 
genio-hyoglossus  and  is  in  contact  with  its  fellow  of  the 
opposite  side.  The  duct  of  Wharton  and  the  lingual  nerve 
are  prolonged  forwards  under  cover  of  the  sublingual 
gland. 

Numerous  small  ducts  (the  number  varying  from  eight 
to  twenty;  proceed  from  the  sublingual  gland.  These  are 
called    the    duds  of  Rivinus,   and    they  all,   as   a   rule,    open 


302  HEAD  AND  NECK 

into  the  mouth  on  the  summit  of  the  plica  sublingualis 
(Birmingham). 

Lingual  Nerve  (nervus  lingualis).  —  In  the  dissection  of 
the  pterygo-maxillary  region,  the  lingual  nerve  has  been  seen 
passing  downwards  between  the  ramus  of  the  mandible  and 
the  internal  pterygoid  muscle.  It  now  inclines  forwards  to 
reach  the  side  of  the  tongue,  and,  passing  over  the  superior 
constrictor  muscle  of  the  pharynx,  it  lies  below  the  last  molar 
tooth  between  the  mucous  membrane  and  the  body  of  the 
mandible.  At  this  point  it  is  in  danger  of  being  hurt  by  the 
clumsy  extraction  of  one  of  the  lower  molars,  and  here  also 
it  may  be  divided  by  the  surgeon,  from  the  inside  of  the 
mouth.  In  its  further  course  the  nerve  keeps  close  to  the 
side  of  the  tongue,  crossing  the  upper  part  of  the  hyoglossus, 
and,  beyond  this,  the  duct  of  Wharton.  It  is  placed  im- 
mediately under  the  mucous  membrane  of  the  mouth,  and  it 
can  be  traced  as  far  as  the  tip  of  the  tongue. 

The  branches  which  proceed  from  the  lingual  nerve  in  this 
region  are  of  two  kinds — (i)  twigs  of  communication;  (2) 
branches  of  distribution. 

C  1.  Two  or  more  to  the  submaxillary  ganglion. 

Twigs  of         I   2.  One    or   two   which   descend   along   the   anterior 

Communication.!  border  of  the  hyoglossus  muscle  to  unite  with 

t  the  hypoglossal  nerve. 

■r,         ,  f  1.   Slender  filaments  to  the  mucous  membrane  of  the 

Branches  ,,        , 

c  I  mouth  and  gums. 

tv  .-••..         ]  2.  A  few  twigs  to  the  sublingual  gland. 
Distribution.  t,         ,       ?    .,     .  &        ^ 

V.  3.   Branches  to  the  tongue. 


The  lingual  branches  pierce  the  substance  of  the  tongue, 
and  then  incline  upwards  to  supply  the  mucous  membrane 
with  the  conical  and  fungiform  papillae  over  the  anterior  two- 
thirds  of  this  organ. 

Submaxillary  Ganglion. — This  is  a  minute  ganglion  which 
will  be  found  lying  upon  the  upper  part  of  the  hyoglossus 
muscle  in  the  interval  between  the  lingual  nerve  and  the  deep 
part  of  the  submaxillary  gland,  under  cover  of  the  mylo-hyoid 
muscle.  In  size  it  is  not  larger  than  the  head  of  a  large  pin, 
and,  when  freed  from  the  connective  tissue  surrounding  both 
it  and  its  branches,  it  will  be  seen  to  be  suspended  from  the 
lingual  nerve  by  two  short  branches,  which  enter  its  upper 
border,  and  are  separated  by  a  distinct  interval.  Of  these, 
the  posterior  connecting  twig  is  frequently  in  the  form  of  two 


SUBMAXILLARY  REGION  303 

or  three  filaments,  which  convey  to  the  ganglion  its  sensory 
and  secretory  roots,  whilst  the  anterior  connecting  branch  must 
be  looked  upon  as  a  twig  given  by  the  ganglion  to  the  lingual 

nerve. 

In  common  with  the  other  ganglia  developed  in  connexion 
with  the  branches  of  the  fifth  cranial  nerve,  this  ganglion  has 
three  roots — viz.,  (1)  a  sensory  root  from  the  lingual  nerve  ;  (2) 
a  secretory  root  from  the  chorda  tympani ;  and  (3)  a  sympathetic 
root  from  the  plexus  around  the  facial  artery. 

From  its  lower  border  several  minute  twigs  proceed,  and 
these  are  distributed — (1)  to  the  submaxillary  gland;  (2)  to 
Wharton's  duct ;  (3)  from  the  branch  which  it  gives  to  the 
lingual  nerve  to  the  sublingual  gland  ;  and  (4)  to  the  mucous 
membrane  of  the  mouth. 

Hypoglossal  Nerve  (nervus  hypoglossus). — This  nerve  has 
been  traced  in  the  dissection  of  the  anterior  triangle  to  the 
point  where  it  disappears  under  cover  of  the  mylo-hyoid 
muscle  (p.  211).  It  is  now  seen  passing  forwards  upon  the 
hyoglossus  muscle  above  the  hyoid  bone,  and  below  the  level 
of  the  deep  part  of  the  submaxillary  gland.  At  the  anterior 
border  of  the  hyoglossus  it  gains  the  surface  of  the  genio- 
hyoglossus  muscle,  into  the  substance  of  which  it  sinks,  and 
finally  breaks  up  into  branches  which  supply  the  muscular 
substance  of  the  tongue.  Upon  the  hyoglossus  muscle  it  is 
accompanied  by  one  of  the  lingual  veins,  frequently  termed 
the  ranine  vein. 

The  branches  which  spring  from  the  hypoglossal  nerve  in 
this  region  are  very  numerous,  and  are  entirely  distributed  to 
muscles.  It  supplies— (1)  the  stylo-glossus;  (2)  the  hyoglossus; 
(3)  the  genio-hyoglossus ;  (4)  the  genio-hyoid  ;  and  (5)  the 
intrinsic  muscles  of  the  tongue. 

In  addition,  it  communicates  freely  with  the  lingual 
nerve.  The  more  apparent  of  these  connexions  take  place 
in  the  form  of  one  or  more  loops  in  relation  to  the  anterior 
border  of  the  hyoglossus.  Other  communications  with  the 
same  nerve  are  effected  in  the  substance  of  the  tongue. 

Reflection  of  the  Hyoglossus. —The  hyoglossus  should  now  be 
carefully  detached  from  the  hyoid  bone,  and  thrown  upwards  towards 
the  tongue.  In  doing  this  there  is  no  need  to  divide  the  structures 
which  lie  upon  its  surface.  By  the  reflection  of  this  muscle  the  follow- 
ing structures  will  be  fully  displayed— (i)  the  second  and  third  stages  of 
the  lingual  artery,  with  its  dorsalis  linguae  branch  and  the  veins  which 
accompany  it;    (2)    the    posterior  part  of  the   genio-hyoglossus;    (3)  the 


304  HEAD  AND  NECK 

origin  of  the  middle  constrictor  of  the  pharynx  ;  and  (4)  the  attachment 
of  the  stylo-hyoid  ligament. 

Genio-hyoglossus  (musculus  genio-glossus). — This  is  a  flat 
triangular  muscle,  the  inner  surface  of  which  is  in  contact 
in  the  mesial  plane  with  its  fellow  of  the  opposite  side.  It 
arises  by  a  short  pointed  tendon  from  the  upper  of  the  two 
genial  tubercles  which  project  from  the  posterior  aspect  of 
the  symphysis  of  the  mandible,  and  from  this  its  fleshy 
fasciculi  spread  out  in  a  fan-shaped  manner.  By  far  the 
greater  part  of  the  muscle  is  inserted  into  the  tongue  by 
an  insertion  which  extends  from  the  tip  backwards  through- 
out the  whole  length  of  the  organ ;  below  the  tongue, 
a  few  fibres  reach  the  side  of  the  pharynx,  whilst  the 
remainder  are  inserted  into  the  body  of  the  hyoid  bone. 
As  we  have  already  noted,  the  genio-hyoglossus  is  supplied 
by  twigs  from  the  hypoglossal  nerve. 

Lingual  Artery  (arteria  lingualis). — As  the  lingual  artery 
is  now  fully  exposed,  it  can  be  conveniently  studied  at  this 
stage.  It  springs  from  the  fore-part  of  the  external  carotid, 
and  it  is  customary  to  describe  it  in  three  parts — viz.,  (1)  a 
part  extending  from  its  origin  to  the  posterior  border  of 
the  hyoglossus  muscle;  (2)  a  part  lying  in  relation  to  the 
upper  border  of  the  hyoid  bone ;  (3)  a  portion  ascending 
under  cover  of  the  anterior  border  of  the  hyoglossus  muscle 
to  the  under  surface  of  the  tongue,  where  it  ends  in  a 
terminal  branch  called  the  ranine  artery  (Fig.  112). 

The  first  part  has  been  fully  examined  in  a  previous 
dissection.  It  lies  in  the  carotid  triangle  of  the  neck,  and 
is  therefore  comparatively  superficial.  It  is  crossed  by  the 
hypoglossal  nerve,  the  tendon  of  the  digastric  and  the 
stylo-hyoid  muscle.  The  second  part  proceeds  forwards 
along  the  upper  border  of  the  great  cornu  of  the  hyoid 
bone,  and  is  covered  by  the  hyoglossus  muscle  which 
intervenes  between  it  and  the  hypoglossal  nerve.  The 
nerve,  however,  is  placed  at  a  slightly  higher  level.  The 
deep  or  internal  relations  of  the  artery  in  this  stage  of  its 
course  are  the  middle  constrictor  of  the  pharynx  and  the 
genio-hyoglossus.  The  third  part  ascends  almost  vertically 
upon  the  genio-hyoglossus.  It  is  overlapped  by  the  an- 
terior border  of  the  hyoglossus,  and  ends  when  it  reaches 
the  under  surface  of  the  tongue  by  turning  forwards  into 
its  terminal  or  ranine  branch. 


SUBMAXILLARY  REGION  305 

The  bra?iches  of  the  lingual  artery  are  : — 

1.  Suprahyoid  from  the  first  part  (p.  237). 

2.  Dorsalis  linguae  from  the  second  part. 

3.  Sublingual  from  the  third  part. 

4.  The  ranine  or  terminal  branch. 

The  dorsalis  lingiice  is  generally  represented  by  two  or 
more  well-marked  branches  (rami  dorsales  linguae)  which 
pass  upwards  under  cover  of  the  hyoglossus  muscle  to  end 
in  twigs  to  the  mucous  membrane  covering  the  back  part 
of  the  dorsum  of  the  tongue.  Some  twigs  are  also  supplied 
to  the  muscular  substance  of  the  organ,  and  a  few  may  be 
traced  backwards  into  the  tonsil. 

The  sublingual  artery  (arteria  sublingualis)  emerges  from 
under  cover  of  the  anterior  border  of  the  hyoglossus,  and  then 
ascends  upon  the  genio-hyoglossus  to  reach  the  sublingual 
gland  which  it  supplies.  It  also  gives  branches  to  the  surround- 
ing muscles,  and  anastomoses  with  its  fellow  of  the  opposite 
side  and  with  the  submental  branch  of  the  facial  artery. 

The  ranine  artery  (arteria  profunda  linguae)  runs  forwards 
upon  the  inferior  aspect  of  the  tongue  as  far  as  the  tip. 
It  can  easily  be  exposed  by  dividing  the  mucous  membrane 
along  its  course,  when  it  will  be  seen  to  lie  close  to  the 
attachment  of  the  frenum  of  the  tongue,  and  to  be  con- 
tinued forwards  in  the  interval  between  the  genio-hyoglossus 
and  the  inferior  lingualis  muscle.  Its  course  is  tortuous  to 
allow  of  the  protrusion  or  elongation  of  the  organ,  and  it 
gives  off  numerous  branches. 

Lingual  Veins. — -The  lingual  artery  is  accompanied  by 
two  small  venae  comites  which  lie  with  it  under  cover  of 
the  hyoglossus ;  but  the  main  vein  of  the  tongue,  termed 
the  ranine,  accompanies  the  hypoglossal  nerve  upon  the 
superficial  surface  of  the  hyoglossus  muscle.  These  veins 
receive  tributaries  corresponding  more  or  less  closely  with  the 
branches  of  the  artery,  and  they  open  into  the  common  facial 
vein,  or  perhaps  directly  into  the  internal  jugular  vein. 

Stylo-hyoid  Ligament. — This  is  the  last  structure  to  be 
examined  in  this  dissection.  It  is  a  fibrous  cord  which 
springs  from  the  tip  of  the  styloid  process  and  passes  down- 
wards and  forwards  to  be  attached  under  cover  of  the  hyo- 
glossus muscle  to  the  lesser  cornu  of  the  hyoid  bone.  It  is 
not  uncommon  to  find  it  partially  ossified  ;  in  other  cases 
it  may  assume  a  ruddy  hue  and  contain  muscular  fibres. 

vol..  11 — 20 


306  HEAD  AND   NECK 


DEEP    DISSECTION    OF    THE    NECK. 

In  the  deep  dissection  of  the  neck  the  following  structures 
are  displayed : — 

i.  The    styloid    process,    with   the  three    muscles    which    take    origin 
from  it. 

2.  The  internal  carotid  artery. 

3.  The  ascending  pharyngeal  artery. 

4.  The  tonsillitic  and  ascending  palatine  branches  of  the  facial  artery. 

5.  The  internal  jugular  vein. 

6.  Glosso-pharyngeal  nerve. 

7.  Vagus  nerve. 

8.  Spinal  accessory  nerve. 

9.  Hypoglossal  nerve. 

10.  The  cervical  part  of  the  sympathetic  cord. 

11.  The  first  loop  of  the  cervical  plexus. 

12.  The  rectus  lateralis  muscle. 

Dissection.  ■ —  Before  the  dissection  is  commenced,  the  skull-cap, 
which,  up  to  the  present  time,  has  been  retained  in  position  by  the  flaps 
of  scalp  stitched  over  it,  should  be  removed.  The  floor  of  the  cranium 
should  then  be  cleansed  by  sponging  it  with  spirit  and  carbolic  solution. 
To  expose  the  styloid  process  and  its  muscles,  it  is  necessary  to  turn  aside 
the  posterior  belly  of  the  digastric,  and  the  external  carotid  artery. 
Detach  the  former  from  its  origin,  and  throw  it  downwards  and  forwards 
towards  the  hyoid  bone.  Its  nerve  of  supply  from  the  facial  must  also 
be  cut ;  and  if  the  filament  which  connects  this  branch  with  the  glosso- 
pharyngeal nerve  has  not  been  previously  seen,  it  should  now  be  sought 
for.  The  external  carotid  artery  may  be  divided  immediately  below  the 
point  where  it  divides  into  its  two  terminal  branches.  After  cutting  the 
occipital  and  posterior  auricular  arteries,  it  can  be  turned  forwards  out  of 
the  way. 

Of  the  parts  in  connexion  with  the  styloid  process,  the  stylo -hyoid 
and  stylo-glossus  muscles  and  the  stylo-hyoid  ligament  have  been  already 
fully  examined;  the  stylo -pharyngeus  muscle  alone  remains  to  be 
described.  In  cleaning  the  fibres  of  this  muscle,  be  careful  not  to  injure 
the  glosso-pharyngeal  nerve  which  appears  at  its  lower  border,  and  gives 
to  it  its  nerve  of  supply. 

Stylo-pharyngeus. — This  is  the  longest  of  the  three  slender 
muscles  which  spring  from  the  styloid  process.  It  arises 
from  its  deep  or  inner  surface  close  to  its  root,  and  extends 
downwards  and  forwards  to  gain  the  side  of  the  pharynx. 
Here  it  disappears  under  cover  of  the  upper  border  of  the 
middle  constrictor  muscle,  and  its  fibres  spread  out,  to  be 
inserted  for  the  most  part  into  the  upper  and  hinder  borders 
of  the  thyroid  cartilage ;  a  certain  proportion,  however,  are 
lost    in    the    wall    of    the    pharynx.       The    stylo-pharyngeus 


DEEP  DISSECTION  OF  THE  NECK  307 

muscle   is    supplied   by  a  branch  from  the  glossopharyngeal 
nerve. 

Dissection.  —  Snip  through  the  base  of  the  styloid  process  with  the 
bone  pliers,  and  throw  it  and  its  attached  muscles  downwards  and 
forwards.  The  internal  carotid  and  ascending  pharyngeal  arteries  may 
now  be  followed  up  to  the  base  of  the  skull.  The  glossopharyngeal, 
vagus,  spinal  accessory,  and  hypoglossal  nerves,  and  the  sicperior  cervical 
ganglion,  with  their  various  connexions  and  branches,  must  at  the  same 
time  be  dissected.  This  is  an  exceedingly  difficult  dissection.  A  dense 
and  tough  fascia  envelops  these  structures,  and  a  great  amount  of 
patience  is  required  to  trace  the  branches  of  the  nerves  through  it.  One 
nerve— the  pharyngeal  branch  of  the  vagus — which  proceeds  downwards 
and  forwards  upon  the  superficial  or  outer  aspect  of  the  internal  carotid, 
is  especially  liable  to  injury,  and  must  therefore  be  borne  in  mind  from 
the  very  outset  of  the  dissection.  The  internal  laryngeal  and  the 
external  laryngeal  jierves  have  been  previously  displayed  in  the  anterior 
triangle  of  the  neck.  These,  if  traced  upwards,  will  lead  to  the  superior 
laryngeal  branch  of  the  vagus,  which  is  carried  downwards  upon  the 
deep  aspect  of  the  internal  carotid  artery.  At  the  base  of  the  skull  all 
the  nerve-trunks  will  be  found  making  their  appearance  close  together  in 
the  interval  between  the  internal  jugular  vein  and  the  internal  carotid 
artery  ;  whilst  behind  the  vein  the  rectus  lateralis  muscle  and  the  first 
loop  of  the  cervical  plexus  will  be  seen. 

Internal  Carotid  Artery  (arteria  carotis  interna). — The 
internal  carotid  artery  is  one  of  the  two  terminal  branches 
of  the  common  carotid,  and  commences  at  the  level  of  the 
upper  border  of  the  thyroid  cartilage.  From  this  point  it 
proceeds  upwards  in  the  neck  in  a  vertical  direction,  until  it 
reaches  the  base  of  the  skull ;  here  it  disappears  from  view  by 
entering  the  carotid  canal  of  the  petrous  portion  of  the 
temporal  bone,  through  which  it  reaches  the  interior  of  the 
cranium.  The  internal  carotid  artery  can  therefore  be  very 
appropriately  divided  into  three  parts — viz.,  (1)  a  cervical; 
(2)  a  petrous;  and  (3)  an  intracranial.  The  cervical  part 
alone  comes  under  the  notice  of  the  student  in  the  present 
dissection. 

In  the  first  instance,  the  internal  carotid  artery  is  placed 
within  the  carotid  triangle,  and  is  therefore  comparatively 
superficial.  It  is  covered  by  the  integument,  platysma,  and 
fascia,  and  is  overlapped  by  the  sterno-mastoid  muscle.  As 
it  proceeds  upwards,  it  gradually  sinks  deeply,  until  it  comes 
to  lie  under  cover  of  the  entire  mass  of  the  parotid  gland,  the 
styloid  process,  the  stylo-pharyngeus  muscle,  the  stylo-hyoid 
muscle,  and  the  posterior  belly  of  the  digastric.  Three  nerves 
and  two  arteries  will  also  be  noticed  to  cross  the  vessel 
superficially,  viz.  :  — 
11 — 20" 


3o8 


HEAD   AND   NECK 


1.  The  occipital  artery. 

2.  The  posterior  auricular  artery. 


1.  The  hypoglossal  nerve. 

2.  The  glosso-pharyngeal  nerve. 

3.  The    pharyngeal    branch    of    the 

vagus  nerve. 

The    relationship    of   the   external    carotid  artery   to   the 

Spinal  accessory- L|     jj|iy — Vagus 

-Ganglion  of  root 

—Glosso-pharyngeal 
Superficial  temporal 


Ganglion 
of  trunk 

Pharyngeal 
branch 


Superior  laryngeal 
Hypoglossal 


Descendens  hypoglossi 

Ascending  pharyngeal 
Internal  carotid 


Internal  maxillary 


External 
carotid 

Posterior 
auricular 


^-Occipital 


Facial 


Lingual 

Branch  to 
thyro-hyoid 
Internal 
laryngeal 


External 
laryngeal 


Common  carotid 


Fig.  116. — Diagram  of  Carotid  System  of  Vessels  in  the  Neck  with  the 
Glosso-pharyngeal,  Vagus,  Spinal  Accessory,  and  Hypoglossal  Nerves. 

internal  carotid  is  a  varying  one.  At  first  the  external 
carotid  lies  in  front  of  it ;  but  soon,  owing  to  its  inclination 
backwards,  it  comes  to  lie  directly  superficial  to  the  internal 


DEEP  DISSECTION  OF  THE  NECK  309 

carotid.      The  following  structures  intervene  between  the  two 
vessels : — 


1.  Styloid  process. 

2.  Stylo-pharyngeus  muscle. 

3.  Glosso-pharyngeal  nerve. 


4.  Pharyngeal  branch  of  vagus. 

5.  A  portion  of  the  parotid  gland. 


Behind,  the  internal  carotid  rests  upon  the  rectus  capitis 
anticus  major  muscle,  and  is  in  contact  with  the  vagus  nerve 
and  the  superior  cervical  ganglion  of  the  sympathetic.  To  its 
outer  side  is  the  internal  jugular  vein.  A  prolongation  upwards 
of  the  carotid  sheath  encloses  the  two  vessels  together  with 
the  vagus  nerve.  On  its  inner  aspect  the  internal  carotid  is 
related  to  the  pharynx  and  the  ascending  pharyngeal  artery. 

Before  leaving  this  vessel,  note  that  at  the  base  of  the 
skull  four  nerves  appear  in  the  interval  between  it  and  the 
internal  jugular  vein ;  these  are  the  glosso-pharyngeal,  the 
vagus,  the  spinal  accessory,  and  the  hypoglossal. 

Ascending  Pharyngeal  Artery  (arteria  pharyngea  ascen- 
dens). — The  origin  of  this  vessel  from  the  external  carotid 
has  already  been  observed  (p.  239).  It  proceeds  vertically 
upwards  to  the  base  of  the  skull,  where  it  ends  by  dividing 
into  minute  meningeal  twigs.  Its  relations  are  very  simple. 
It  is  placed  between  the  internal  carotid  artery  and  the  wall 
of  the  pharynx,  and  this  position  it  holds  throughout  its 
entire  course. 

The  following  branches  will  be  recognised  as  springing 
from  the  ascending  pharyngeal : —  ^ 

1.  Pharyngeal. 

2.  Prevertebral. 

3.  Meningeal. 

The  pharyngeal  branches  (rami  pharyngei)  supply  the 
pharynx,  and  the  lower  members  of  the  series  anastomose 
with  the  superior  thyroid  artery.  Higher  up,  a  larger  palatine 
branch  distributes  twigs  to  the  Eustachian  tube,  the  soft  palate, 
and  the  tonsil. 

The  prevertebral  branches  are  small  twigs  which  are  given 
to  the  prevertebral  muscles,  and  anastomose  with  the  ascending 
cervical  artery. 

The  meningeal  twigs  enter  the  cranium  through  three 
openings,  viz.,  the  foramen  lacerum  medium,  the  jugular 
foramen,  and  the  anterior  condyloid  foramen. 

Inferior  Palatine  and  Tonsillitic  Arteries. — At  this  stage 
the   dissector  should   again   examine   these   vessels — the   first 

11— 205 


3io  HEAD  AND  NECK 

branches  which  are  given  off  by  the  facial  artery.  They  have 
already  been  described  (p.  237),  but  their  relations  as  they 
ascend  in  the  neck  can  now  be  more  satisfactorily  studied. 
The  size  of  the  inferior  or  ascending  palatine  is  very  variable, 
and  depends  very  much  upon  that  of  the  palatine  branch  of 
the  ascending  pharyngeal. 

Internal  Jugular  Vein  (vena  jugularis  interna).  —  The 
internal  jugular  vein  is  the  largest  venous  channel  of  the 
neck.  It  is  directly  continuous  with  the  lateral  sinus  of  the 
cranial  cavity,  and  it  enters  the  neck  through  the  posterior 
compartment  of  the  jugular  foramen.  From  this  it  proceeds 
downwards,  until  it  reaches  the  posterior  aspect  of  the  inner 
end  of  the  clavicle,  where  it  joins  the  subclavian  vein  to  form 
the  innominate  or  brachio-cephalic  vein.  Its  commencement 
in  the  jugular  foramen  shows  a  slight  dilatation,  termed  the 
bulb,  the  lumen  of  which  remains  at  all  times  patent  owing  to 
the  connexion  of  its  walls  to  the  margins  of  the  foramen. 
By  passing  a  probe  from  the  lateral  sinus  into  the  internal 
jugular  vein,  the  continuity  of  the  two  channels  can  be  easily 
demonstrated. 

The  relations  which  the  internal  jugular  vein  presents  in 
the  neck  can  be  summed  up  in  a  very  few  words.  At  the 
base  of  the  skull  it  lies  behind  the  internal  carotid  artery,  and 
rests  upon  the  rectus  lateralis  muscle.'  Very  soon,  however, 
it  changes  its  relationship  to  the  internal  carotid,  and  comes 
to  lie  upon  its  outer  side.  This  position  it  maintains  until  it 
reaches  the  upper  border  of  the  thyroid  cartilage.  Below 
this  level  it  is  continued  downwards  upon  the  outer  side  of 
the  common  carotid  artery. 

Throughout  its  whole  length  it  is  included  within  a  sheath 
of  fascia  common  to  it,  the  two  arteries  along  which  it  lies, 
and  the  vagus  nerve.  Lastly,  at  the  root  of  the  neck,  its 
terminal  part  crosses  the  first  portion  of  the  subclavian  artery. 

But  there  are  some  slight  differences  to  be  noted  between 
the  two  veins  of  opposite  sides.  The  right  vein  is  usually 
considerably  the  larger  of  the  two,  and  as  they  approach  the 
root  of  the  neck  both  veins  incline  slightly  to  the  right.  From 
this  it  follows  that  the  left  vein  is  closely  applied  to  the  lower 
portion  of  the  common  carotid  artery  of  that  side,  whilst  the 
right  vein  is  separated  from  its  companion  artery  by  a  narrow 
interval  which  presents  a  triangular  figure.  The  base  of  this 
triangle  is  formed  by  the  first  part  of  the  subclavian  artery, 


DEEP  DISSECTION  OF  THE  NECK 


311 


and  it  is  bisected  by  the  vagus  nerve.  It  should  also  be 
remembered  that  on  the  left  side  the  terminal  part  of  the 
thoracic  duct  passes  behind  the  internal  jugular  vein. 

The  tributaries  which  join  the  internal  jugular  vein  have 
for  the  most  part  been  previously  studied.     They  are  : — 


1.  Inferior  petrosal  sinus  (p.  129). 

2.  Pharyngeal  veins. 

3.  Lingual  veins  (p.  305). 

4.  Common  facial  vein  (p.  238). 

5.  Superior  thyroid  vein  (p.  236). 


6.  Middle  thyroid  vein  (p.  242). 

7.  Thoracic    duct  on    the  left  side 

and  the   right  lymphatic  duct 
on  the  right  side  (p.  224). 


The   inferior  petrosal  sinus  leaves   the  cranial   cavity  by  the 
anterior  compartment  of  the  jugular  foramen,  and  joins  the 


Sheath  of  dura  mater 

around  vagus  and  spinal 

accessory  nerves 


Ganglion  of  trunk 
Internal  jugular  vein 

Superior  laryngeal  nerve 
Spinal  accessory  nerve 


r^ft 


Vagus  nerve 


Sheath  of  dura  mater  around 
glosso-pharyngeal  nerve 

Inferior  petrosal  sinus 
Internal  carotid  artery 


Glosso-pharyngeal  nerve 


Pharyngeal  branch  of 
vagus. 


Internal  laryngeal  nerve 
External  laryngeal  nerve 


FlG.117. — Diagram  of  the  relation  of  parts  in  the 
Jugular  Foramen. 

fore-part  of  the  internal  jugular  vein  close  to  the  base  of 
the  skull.  By  passing  a  probe  from  the  interior  of  the  skull 
through  the  sinus,  its  connexion  with  the  vein  can  readily  be 
made  out. 

The  pharyngeal  tributaries  join  the  internal  jugular  about 
the  level  of  the  hyoid  bone.  They  come  from  a  venous 
plexus  which  lies  upon  the  side  of  the  pharynx,  and  presents 
free  communications  above  with  the  pterygoid  plexus. 

Dissection.— The  internal  jugular  vein  should  now  be  slit  open.  A 
short  distance  above  its  termination  a  single  or  a  double  flapped  valve 
will  be  discovered.  The  vein  should  then  be  divided  about  two  inches 
below  its  commencement  and  its  upper  part  thrown  upwards.  This  is 
done  to  enable  the  dissector  to  obtain  a  better  view  of  the  hypoglossal 
nerve  as  it  issues  from  the  anterior  condyloid  foramen, 
ir— 20  c 


312 


HEAD  AND  NECK 


Glossopharyngeal,  Vagus  or  Pneumogastric,  and  Spinal 
Accessory  Nerves. — These  nerves  have,  on  a  previous 
occasion,  been  seen  leaving  the  cranial  cavity  through  the 
middle  compartment  of  the  jugular  fossa,  in  the  interval 
between  the  commencement  of  the  internal  jugular  vein 
behind  and  the  inferior  petrosal  sinus  in  front  (p.  126,  and 
Fig.  60,  p.  125).  It  is  well  that  the  dissector  should  again 
examine   the   interior   of  the   cranial   cavity  and  refresh  his 


Oculo-motor  nerve 


Trochlear  nerve 

Sensory  root  of  the  trigeminal  nerve 
Motor  root  of  the  trigeminal 
-^         nerve 


\bducent  nerve 

Facial  nerve 

1 


Cut  edge  of  the 
tentorium 


-.Pars  inter- 
media 
Auditory  nerve 

Right  lateral  sinus 

Glosso-pharyngeal 
nerve 
Vagus  nerve 
Spinal  accessory  nerve 

S8#'   Jf^  Vertebral  artery 
>       jff^ Hypoglossal  nerve 
First  spinal  nerve 
^Spinal  accessory  nerve 

FiG.  118. — Section  through  the  Head  a  little  to  the  right  of  the  Mesial 
Plane.  It  shows  the  posterior  cranial  fossa  and  the  upper  part  of  spinal 
canal  after  the  removal  of  the  brain  and  the  cord. 

memory  as  to  the  manner  in  which  they  enter  the  foramen. 
The  glossopharyngeal  occupies  the  foremost  position,  and  it  is 
cut  off  from  the  others  by  possessing  a  special  and  separate 
tube-like  sheath  of  dura  mater.  The  spinal  accessory  is  placed 
behind  the  vagus,  and  both  are  included  within  the  same 
sheath  of  dura  mater.  They  therefore  traverse  the  foramen 
in  close  contact  with  each  other.  Reaching  the  exterior  of 
the  skull,  the  three  nerves  at  first  lie,  together  with  the  hypo- 
glossal nerve,  in  the  interval  between  the  internal  jugular  vein 
and  the  internal  carotid  artery,  but  soon  they  choose  different 


DEEP  DISSECTION  OF  THE  NECK  313 

routes.  The  spitial  accessory  inclines  backwards  over  or 
behind  the  internal  jugular  vein  ;  the  glosso-pharyngeal  inclines 
forwards  over  the  internal  carotid ;  whilst  the  vagus  proceeds 
vertically  downwards  between  these  vessels  (Fig.  117). 

In  an  ordinary  dissection  it  is  impossible  to  follow  out  many  of  the 
minute  twigs  which  take  origin  from  these  nerves  in  the  region  of  the 
basis  cranii.  To  do  so  it  is  necessary  to  possess  a  perfectly  fresh  part, 
which  has  been  specially  prepared  by  having  the  soft  parts  toughened  with 
spirit  and  the  bone  softened  by  immersion  in  a  weak  solution  of  acid. 
Even  then  the  dissection  is  a  difficult  one,  although  it  should  certainly  be 
undertaken  by  the  advanced  student  in  the  event  of  his  being  able  to  obtain 
a  part  for  the  purpose. 

In  the  following  description  of  these  nerves  the  account 
of  the  branches  which  can  in  all  cases  be  traced  is  printed 
in  large  type,  whilst  that  of  those  requiring  special  dissection 
is  printed  in  small  type. 

Glosso-pharyngeal  Nerve  (nervus  glosso-pharyngeus). — The 
glosso-pharyngeal  nerve  inclines  downwards  and  forwards  and 
crosses  the  internal  carotid  artery  superficially.  It  passes 
under  cover  of  the  styloid  process  and  the  stylo-pharyngeus 
muscle,  and  at  the  lower  border  of  the  latter  it  hooks  round 
the  muscle  and  then  curves  forwards  upon  its  superficial 
surface  to  gain  the  base  of  the  tongue.  In  the  dissection  of 
the  submaxillary  region,  its  terminal  part  has  been  seen 
disappearing  under  cover  of  the  posterior  border  of  the 
hyoglossus  muscle;  here  it  ends  in  lingual  branches. 

In  the  present  dissection  the  following  branches  should  be 
made  out : — 


1.  Communicating    branch    from 

the  facial. 

2.  Nerve  to  the  stylo-pharyngeus. 


3.  Pharyngeal. 

4.  Tonsillitic. 

5.  Lingual. 


The  conwiunicating  branch  from  the  facial  springs  from  the 
nerve  to  the  posterior  belly  of  the  digastric,  and,  as  a  rule, 
emerges  from  midst  the  fibres  of  this  muscle  to  join  the 
glosso-pharyngeal  close  to  the  lower  part  of  the  jugular 
foramen. 

The  stylopharyngeal  nerve  is  a  small  twig  which  enters  the 
muscle  of  the  same  name.  The  greater  part  of  its  fibres, 
however,  arc  continued  through  the  muscle  to  the  mucous 
membrane  of  the  pharynx. 

'I he  pharyngeal  branches  consist — (1)  of  one  or  two  small 
twigs  which  perforate  the  superior  constrictor  to  reach  the 
mucous  membrane  of  the  pharynx;  and  (2)  a  larger  nerve 


3i4  HEAD  AND  NECK 

which  comes  off  higher  up  and  joins  the  pharyngeal  branch 
of  the  vagus  to  form  the  pharyngeal  plexus.  It  frequently 
divides  into  two  or  more  branches. 

The  tonsillitic  branches  proceed  from  the  glosso-pharyngeal 
near  the  base  of  the  tongue.  They  form  a  plexus  over  the 
tonsil,  termed  the  circulus  tonsillaris,  and  give  twigs  to  the 
mucous  membrane  of  the  isthmus  faucium  and  the  soft 
palate. 

The  terminal  or  lingual  brandies  will  be  followed  in  the 
dissection  of  the  tongue. 

There  are  still  other  points  in  connexion  with  the  glosso-pharyngeal 
nerve  which  require  mention.  At  the  lower  part  of  the  jugular  foramen 
two  small  ganglia  are  formed  upon  its  trunk,  and  from  the  lower  of  these 
certain  minute  branches  are  given  off.  The  upper  ganglion  is  called  the 
jugular  ganglion  ;  the  lower  one  is  termed  the  petrous  ganglion. 

The  jugular  ganglion  is  a  minute  ganglionic  swelling,  which  only 
involves  a  portion  of  the  fibres  of  the  nerve-trunk,  and  is  placed  in  the 
upper  part  of  the  bony  groove  in  which  the  nerve  lies  as  it  proceeds  through 
the  jugular  foramen.     No  branches  arise  from  it. 

The  petrous  ganglion  is  a  larger  swelling,  which  involves  the  entire 
nerve-trunk,  and  lies  at  the  opening  of  the  jugular  foramen  between  the 
inferior  petrosal  sinus  (which  intervenes  between  it  and  the  anterior  border 
of  the  foramen)  and  the  vagus  nerve  invested  by  its  fibrous  sheath  derived 
from  the  dura  mater.  Its  length  is  not  more  than  two  or  three  lines. 
Three  branches  of  communication  enter  or  proceed  from  it.  These  connect 
it  with — (i)  the  superior  cervical  sympathetic  ganglion;  (2)  the  auricular 
branch  of  the  vagus  ;  and  (3)  the  root-ganglion  of  the  vagus. 

In  addition  to  these  twigs  the  tympanic  nerve  or  the  nerve  of  Jacob  son 
takes  origin  from  the  petrous  ganglion. 

Tympanic  Nerve. — The  ultimate  destination  of  this  nerve  may  be 
regarded  as  being  the  otic  ganglion,  but  it  takes  a  very  circuitous  route 
to  gain  this  structure.  It  enters  a  small  foramen  on  the  ridge  which 
separates  the  jugular  fossa  from  the  carotid  foramen  on  the  under  surface 
of  the  petrous  bone,  and  it  is  conducted  by  a  narrow  canal  to  the  tympanic 
cavity.  It  traverses  the  inner  wall  of  this  chamber,  grooving  the  promon- 
tory. Having  gained  the  anterior  part  of  the  tympanum,  it  enters  the 
bone  a  second  time,  and  runs  in  a  minute  canal,  which  tunnels  the  petrous 
bone  below  the  upper  end  of  the  channel  in  which  is  lodged  the  tensor 
tympani  muscle.  In  this  part  of  its  course  the  tympanic  nerve  is  joined  by 
a  branch  from  the  geniculate  ganglion  of  the  facial  nerve,  and,  after  the 
junction  is  effected,  it  is  termed  the  small  superficial  petrosal  nerve. 

The  canal  in  which  the  small  supeificial  petrosal  nerve  is  lodged  opens 
into  the  cranial  cavity  upon  the  anterior  face  of  the  petrous  bone, 
immediately  external  to  the  hiatus  Fallopii.  Through  this  the  nerve 
emerges,  and  soon  leaves  the  interior  of  the  cranium  by  passing  down- 
wards in  the  interval  between  the  great  wing  of  the  sphenoid  and  the 
petrous  bone.     Outside  the  skull  it  ends  by  joining  the  otic  ganglion. 

In  the  tympanic  cavity  the  tympanic  nerve  gives  branches  of  supply 
— (1)  to  the  mucous  membrane  of  the  tympanum;  (2)  to  the  lining 
membrane  of  the  mastoid  cells  ;  and  (3)  to  the  mucous  membrane  of  the 
Eustachian  tube.  It  also  gives  off  a  fine  branch  termed  the  small  deep 
eptrosal  ne>i>e  (n.  petrosus  profundus  minor).     This  enters  a  canal  in  the 


DEEP  DISSECTION  OF  THE  NECK  315 

processus  cochleariformis  which  conducts  it  to  the  foramen  lacerum  medium, 
where  it  effects  a  junction  with  the  carotid  plexus.  The  tympanic  nerve 
likewise  receives  a  minute  twig  from  the  carotid  plexus  which  is  called  the 
nervus  carotico-tympcuiicus. 

Vagus  or  Pneumogastric  Nerve. — The  vagus  passes  through 
the  middle  compartment  of  the  jugular  foramen  in  company 
with  the  spinal  accessory — both  being  included  within  the  same 
sheath  of  dura  mater.  In  the  neck  it  pursues  a  vertical 
course,  lying,  in  the  first  instance,  between  the  internal  jugular 
vein  and  the  internal  carotid  artery,  and  afterwards  between 
the  same  vein  and  the  common  carotid  artery.  Further,  as 
has  been  already  observed,  it  is  enclosed  within  the  sheath 
which  envelops  these  vessels,  and  it  lies  upon  a  plane  posterior 
to  them.  At  the  root  of  the  neck  it  enters  the  thorax,  and 
shows  different  relations  on  the  two  sides.  On  the  right  side 
it  crosses  the  first  part  of  the  subclavian  artery ;  on  the  left 
side  it  proceeds  dowrnwards  between  the  common  carotid  and 
left  subclavian  arteries,  and  passes  under  cover  of  the  left 
innominate  vein. 

As  in  the  case  of  the  glossopharyngeal,  the  vagus  shows 
two  ganglia  in  connexion  with  its  upper  part.  These  are 
the  ganglion  of  the  root  (ganglion  jugulare)  and  the  ganglion  of 
the  trunk  (ganglion  nodosum). 

The  Ganglion  of  the  Root  is  situated  within  the  jugular  foramen.  It 
is  a  rounded  swelling  which  is  connected  by  communicating  twigs  with 
several  of  the  nerves  in  the  neighbourhood,  and  which  gives  off  two 
branches  of  distribution. 


Branches  of  Communication. 

Branches  of  Distribution. 

1.  With  the  facial  nerve. 

2.  With  the  petrous   ganglion 

of  the  glosso-pharyngeal. 

3.  With  the  spinal  accessory. 

4.  With  the  superior  ganglion 

of  the  sympathetic. 

1.  Recurrent  nerve. 

2.  Auricular  nerve. 

The  recurrent  branch  is  a  minute  twig  which  runs  backwards  through 
the  jugular  foramen,  and,  dividing  into  two  branches,  is  distributed  to 
the  dura  mater  in  the  posterior  cranial  fossa. 

The  auricular  nerve  (Arnold's  nerve)  obtains  a  filament  of  communica- 
tion from  the  petrous  ganglion  of  the  glosso- pharyngeal,  and  proceeds 
backwards  upon  the  outer  surface  of  the  bulb  of  the  internal  jugular  vein 
to  enter  a  minute  aperture  on  the  posterior  part  of  the  outer  wall  of  the 


3i6  HEAD  AND  NECK 

jugular  foramen.  A  narrow  canal  now  conducts  it  through  the  substance 
of  the  temporal  bone,  and,  on  its  way,  it  crosses  internal  to  the  Fallopian 
canal  a  short  distance  above  the  stylo-mastoid  foramen.  It  is  thus  brought 
into  close  relation  with  the  facial  nerve,  and  is  connected  with  it  by  an 
ascending  and  a  descending  branch  of  communication.  Penally,  it  appears 
on  the  surface  of  the  skull  in  the  interval  between  the  mastoid  process  and 
the  external  auditory  meatus.      Its  further  course  is  described  on  p.  262. 

Ganglion  of  the  Trunk. — After  emerging  from  the  jugular 
foramen,  the  vagus  nerve  is  joined  by  the  accessory  porlio?i  of 
the  spinal  accessory  nerve,  and  swells  out  into  the  ganglion  of 
the  trunk. 

The  gang/ion  of  the  trunk  is  an  elongated  reddish-coloured 
swelling  of  about  three-quarters  of  an  inch  in  length,  which  is 
developed  upon  the  stem  of  the  vagus  nerve  half  an  inch 
below  the  base  of  the  cranium.  Strong  branches  of  com- 
munication pass  between  this  ganglion,  the  first  loop  of  the 
cervical  plexus,  and  the  superior  cervical  ganglion  of  the 
sympathetic.  Further,  the  hypoglossal  nerve  is  generally 
closely  bound  to  it  by  fibrous  attachment,  in  the  midst  of 
which  some  interchange  of  nerve  filaments  takes  place. 

Branches  of  Distribution  of  the  Cervical  Part  of  the 
Vagus. — The  branches  which  spring  from  the  vagus  as  it 
traverses  the  neck  are  the  following : — 

1.  Pharyngeal. 

2.  Superior  laryngeal. 

3.  Inferior  or  recurrent  laryngeal. 

4.  Cardiac. 

Pharyngeal  Branch  (ramus  pharyngeus). — This  springs 
from  the  upper  part  of  the  ganglion  of  the  trunk,  and  runs 
downwards  and  forwards,  superficial  to  the  internal  carotid 
artery,  to  end  in  the  pharyngeal  plexus.  Very  frequently  it  is 
replaced  by  two  branches,  of  which  the  upper  is  the  larger. 

Superior  Laryngeal  Nerve  (nervus  laryngeus  superior). — 
This  is  a  much  larger  branch,  which  takes  origin  from  the 
middle  of  the  same  ganglion.  It  passes  downwards  and 
forwards,  but  differs  from  the  preceding  nerve  by  passing 
tinder  cover  of  the  internal  carotid  artery.  In  this  situation 
it  ends  by  dividing  into  the  internal  laryngeal  and  external 
laryngeal  nerves ;  both  of  these  have  been  previously  seen  in 
the  dissection  of  the  anterior  triangle  (p.  203).  Before  it 
divides,  the  superior  laryngeal  effects  communications  by 
means  of   fine  twigs  with   the  superior  cervical  ganglion   of 


DEEP  DISSECTION  OF  THE  NECK  317 

the  sympathetic,  and  it  also  receives  one  or  two  filaments 
from  the  pharyngeal  plexus. 

The  internal  laryngeal  nerve  runs  forwards  to  the  interval 
between  the  hyoid  bone  and  the  thyroid  cartilage,  and,  dis- 
appearing under  cover  of  the  posterior  border  of  the  thyro- 
hyoid muscle,  it  pierces  the  membrane  of  the  same  name,  and 
enters  the  larynx. 

The  external  laryngeal  nerve  is  a  very  slender  branch,  which 
inclines  downwards  and  forwards  to  reach  the  crico-thyroid 
muscle  in  which  it  ends.  It  supplies  a  few  filaments  to  the 
inferior  constrictor  of  the  pharynx  and  a  fine  twig  to  the 
superior  cardiac  branch  of  the  sympathetic,  whilst  it  receives 
a  communicating  branch  from  the  superior  cervical  ganglion 
of  the  sympathetic. 

Recurrent  Laryngeal  Nerve  (nervus  laryngeus  inferior).— 
The  recurrent  laryngeal  arises  differently  on  the  two  sides. 
On  the  right  side,  it  springs  from  the  vagus  as  it  crosses  the 
first  part  of  the  subclavian  artery,  and  it  adopts  its  recurrent 
course  by  hooking  round  this  vessel.  On  the  left  side,  it 
arises  in  the  thorax,  and  hooks  round  the  aortic  arch  (or, 
more  correctly  speaking,  around  the  termination  of  the  ob- 
literated ductus  arteriosus).  In  the  neck  each  nerve  ascends 
in  the  groove  between  the  trachea  and  oesophagus,  and 
passing  behind  or  in  front  of  the  inferior  thyroid  artery,  or  it 
may  be  between  the  two  terminal  branches  of  this  artery,  it 
disappears  under  cover  of  the  lower  border  of  the  inferior 
constrictor  muscle,  to  enter  the  larynx. 

Before  the  recurrent  laryngeal  nerve  reaches  the  larynx  it 
gives  off  several  branches — viz.,  (1)  cardiac  branches  ;  (2)  twigs 
to  the  trachea  and  oesophagus ;  and  (3)  a  few  filaments  to  the 
inferior  constrictor  as  it  passes  under  cover  of  its  lower  margin. 

Cardiac  Branches. — Two  cardiac  branches  arise  from  the 
vagus  in  the  neck.  On  the  right  side,  both  of  these  enter 
the  thorax  by  passing  behind  the  subclavian  artery  and  end 
in  the  deep  cardiac  plexus.  On  the  left  side,  the  upper  nerve 
joins  the  deep  cardiac  plexus,  whilst  the  lower  nerve  enters 
into  the  formation  of  the  superficial  cardiac  plexus. 

Spinal  Accessory  Nerve  (nervus  accessorius). — This  nerve 
consists  of  two  parts — an  accessory  and  a  spinal.  In  the 
foramen  jugulare  the  accessory  portio?i  is  connected  by  one  or 
two  fine  twigs  with  the  root-ganglion  of  the  vagus,  and  below 
the  basis  cranii  it  leaves  the  spinal  part  and  joins  the  vagus. 


0 


1 8  HEAD  AND  NECK 


The  accessory  part  of  the  spinal  accessory  nerve  contributes  to  the 
vagus  the  greater  proportion  of  its  motor  fibres.  They  pass  over  the 
surface  of  the  trunk-ganglion,  and  are  continued  into  the  pharyngeal  and 
into  the  superior  laryngeal  nerves.  Some  of  the  fibres  are  likewise  carried 
down  the  stem  of  the  vagus  into  the  cardiac  branches  and  also  into  the 
recurrent  laryngeal  nerve. 

The  spinal  part  of  the  spinal  accessory  is  directed  back- 
wards under  the  transverse  process  of  the  atlas.  It  crosses 
the  internal  jugular  vein,  and  disappears  into  the  substance 
of  the  sterno-mastoid  muscle.  Its  further  course  has  been 
already  studied  (pp.  137  and  203).  It  is  distributed  to  two 
muscles — viz.,  the  sterno-mastoid  and  the  trapezius. 

Pharyngeal  Plexus  (plexus  pharyngeus). — This  is  a  mesh- 
work  of  fine  nerve  filaments,  which  is  formed  upon  the  lateral 
wall  of  the  pharynx  at  the  level  of  the  middle  constrictor 
muscle.  The  pharyngeal  branches  of  the  vagus,  glosso- 
pharyngeal, and  superior  cervical  ganglion  of  the  sympathetic 
enter  into  its  construction,  and  one  or  more  minute  ganglia 
are  developed  in  connexion  with  it.  Its  terminal  twigs  are 
given  to  the  muscles  and  mucous  membrane  of  the  pharynx, 
and  one  branch  (the  ra??ius  lingualis  vagi)  connects  the  plexus 
with  the  hypoglossal  nerve. 

Hypoglossal  Nerve  (nervus  hypoglossus). — The  hypoglossal 
nerve  makes  its  exit  from  the  cranium,  through  the  anterior 
condyloid  foramen.  It  pierces  the  dura  mater  in  tw7o  separate 
parts,  which  unite  into  one  stem  at  the  entrance  of  the  bony 
foramen.  As  it  issues  from  the  anterior  condyloid  foramen  it 
lies  deeply  under  cover  of  the  internal  jugular  vein  and  the 
internal  carotid  artery ;  but  it  almost  immediately  inclines  out- 
wards, and,  taking  a  half  spiral  turn  around  the  trunk-ganglion 
of  the  vagus,  it  appears  between  the  two  vessels,  and  is 
continued  downwards  and  forwards.  Its  close  connexion 
with  the  ganglion  of  the  trunk  of  the  vagus  has  already  been 
noted.  The  two  nerves  at  this  point  are  almost  inseparably 
united  by  dense  connective  tissue,  and  in  the  midst  of  this  an 
interchange  of  nerve  fibres  takes  place.  Gaining  the  lower 
border  of  the  posterior  belly  of  the  digastric  muscle,  the  hypo- 
glossal nerve  hooks  round  the  occipital  artery,  and  enters  the 
anterior  triangle  of  the  neck.  From  this  point  to  the  under 
surface  of  the  tongue  it  has  already  been  traced. 

Brandies  of  communication. — Near  the  base  of  the  skull  the 
hypoglossal  is  brought  into  connexion  with  (1)  the  superior 
cervical  ganglion  ;  (2)  the  vagus  j   and  (3)  the  first  cervical 


DEEP   DISSECTION  OF  THE  NECK  319 

nerve.  Further,  as  it  turns  round  the  occipital  artery  it  receives 
the  ramus  lingualis  vagi  from  the  pharyngeal  plexus. 

The  importance  of  the  connexion  between  the  hypoglossal 
and  the  first  cervical  nerve  has  already  been  referred  to  (p.  227, 
Fig.  87). 

Branches  of  distribution. — With  the  exception  of  the  minute 
recurrent  and  vascular  twigs,  which  come  off  within  the  con- 
dyloid foramen,  the  branches  of  distribution  which  proceed 
from  the  hypoglossal  nerve  have  been  described  (pp.  211 
and  303). 

The  recurrent  branch  arises  in  the  upper  part  of  the  anterior  condyloid 
foramen,  and,  regaining  the  interior  of  the  cranium,  it  is  distributed  to  the 
dura  mater  around  the  foramen  magnum. 

The  vascular  twigs  are  some  fine  filaments,  which  are  said  to  be  supplied 
to  the  deep  aspect  of  the  internal  jugular  vein. 

Dissection. — In  the  dissection  of  the  neck  the  greater  part  of  the  cervical 
sympathetic,  with  the  branches  which  proceed  from  it,  has  been  displayed. 
The  inferior  ganglion,  which  lies  deeply  in  the  hollow  between  the 
transverse  process  of  the  seventh  cervical  vertebra  and  the  neck  of  the  first 
rib,  is  still  to  a  certain  extent  concealed,  and  must  now  be  displayed. 
Dislodge  the  subclavian  artery  from  its  place  on  the  first  rib  behind  the 
scalenus  anticus  muscle,  and  turn  it  well  inwards.  To  do  this  efficiently, 
it  will  be  necessary  to  cut  the  superior  intercostal  artery  at  its  origin  ;  this 
vessel  runs  downwards  upon  the  outer  side  of  the  sympathetic.  Great  care 
must  be  taken  to  preserve  uninjured  the  fine  nerves  which  proceed  down- 
wards in  front  of  the  first  part  of  the  subclavian  artery.  If  more  space  for 
the  dissection  is  required,  the  fore-part  of  the  first  rib  may  be  removed  by 
the  bone-pliers,  but,  as  a  general  rule,  this  will  not  be  found  to  be  necessary. 

Sympathetic  Cord  in  the  Neck. — The  number  of  ganglia 
which  are  developed  upon  the  sympathetic  cord  in  the  neck  is 
reduced  to  three,  and  no  white  rami  com?mtnica?ites  enter  either 
the  cord  or  the  ganglia  from  the  cervical  spinal  nerves. 

The  sympathetic  cord  takes  a  vertical  course  through  the 
neck  in  front  of  the  roots  of  the  transverse  processes  of  the 
vertebrae.  It  lies  upon  the  rectus  capitis  anticus  major  and 
the  longus  colli  muscles,  and  is  embedded  in  the  posterior 
wall  of  the  carotid  sheath.  Above,  it  is  prolonged  upwards  in 
the  form  of  a  stout,  ascending  nerve-trunk,  which  accompanies 
the  internal  carotid  artery  into  the  carotid  canal ;  be/ozv,  it 
becomes  continuous  over  the  neck  of  the  first  rib  and  behind 
the  subclavian  artery  with  the  thoracic  portion  of  the 
sympathetic.  The  branches  take  origin  from  the  ganglia  ; 
occasionally,  however,  one  or  more  may  be  observed  to  arise 
from  the  connecting  cords. 

Superior  Cervical  Ganglion  (ganglion  cervicale  superius). — 


32o  HEAD  AND  NECK 

This  is  the  largest  of  the  three  ganglia.  It  is  an  elon- 
gated fusiform  body  which  varies  somewhat  in  size.  It  is 
placed  upon  the  upper  part  of  the  rectus  capitis  anticus  major, 
opposite  the  second  and  third  vertebrae,  and  behind  the 
internal  carotid  artery.  From  its  upper  end  the  stout  branch 
proceeds  which  enters  the  carotid  canal,  whilst  its  lower  end 
tapers  into  the  downward  continuation  of  the  cord.  Numerous 
branches  issue  from  it ;  of  these  some  connect  it  with  neigh- 
bouring nerves,  whilst  others  are  distributed  in  various  ways. 

The  connecting  branches  are:  —  (i)  slender  grey  rami 
cotmnunicantes  which  connect  it  with  the  upper  four  cervical 
nerves  ;  (2)  twigs  to  both  ganglia  of  the  vagus ;  (3)  to  the 
petrous  ganglion  of  the  glosso  -  pharyngeal ;  and  (4)  to  the 
hypoglossal.     It  is  not  connected  with  the  spinal  accessory. 

The  branches  of  distribution  are  : — 

1.  Rami  vasculares. 

2.  Pharyngeal. 

3.  Superior  cardiac. 

The  rami  vasculares  (nervi  carotici  externi)  are  soft  delicate 
filaments  which  run  towards  the  external  carotid  artery,  and 
form  a  loose  interlacement  around  it  and  its  branches.  From 
this  plexus  a  branch  is  given  to  the  carotid  body  ;  further, 
the  part  continued  upon  the  facial  artery  supplies,  as  we  have 
already  noted,  the  sympathetic  root  to  the  submaxillary 
ganglion,  whilst  the  subdivision  upon  the  middle  meningeal 
artery  furnishes  the  corresponding  root  to  the  otic  ganglion, 
as  well  as  the  external  superficial  petrosal  nerve  which  runs  to 
the  geniculate  ganglion  of  the  facial  nerve. 

The  pharyngeal  branches  course  inwards  between  the  two 
carotid  arteries  to  join  the  pharyngeal  plexus. 

The  superior  cardiac  nerve  (nervus  cardiacus  superior)  is  a 
long  slender  branch  which  springs  by  several  roots  from  the- 
ganglion  and  then  proceeds  downwards  behind  the  carotid 
artery.  At  different  stages  of  its  course  it  is  joined  by  other 
branches  of  the  sympathetic,  by  a  branch  from  the  vagus,  and 
also  by  filaments  from  the  external  laryngeal  and  recurrent 
laryngeal  nerves.  The  right  superior  cardiac  nerve  is  continued 
into  the  thorax  by  passing  behind  or  in  front  of  the  subclavian 
artery,  and  it  ends  in  the  deep  cardiac  plexus.  The  left  superior 
cardiac  nerve  follows  the  left  common  carotid  artery  in  the 
thorax,  and,  crossing  the  arch  of  the  aorta,  ends  in  the 
superficial  cardiac  plexus. 


DEEP  DISSECTION  OF  THE  NECK  321 

Middle  Cervical  Ganglion  (ganglion  cervicale  medium). — 
This  ganglion  is  the  smallest  of  the  three  ganglia  of  the 
neck.  It  is  placed  opposite  the  sixth  cervical  vertebra  in 
close  proximity  to  the  inferior  thyroid  artery,  upon  which, 
indeed,  it  not  infrequently  rests.  It  presents  the  following 
branches  : — 

1.  Grey  rami  communicantes  which  connect  it  with  the  fifth  and  sixth 

spinal  nerves,  and  which  pass  between  the  contiguous  margins  of 
the  scalenus  anticus  and  longus  colli  muscles. 

2.  Thyroid  branches  which  run  to  the  thyroid  body  along  the  inferior 

thyroid  artery,  and  which  form  connexions  with  the  external  and 
recurrent  larnygeal  nerves. 

3.  The  middle  cardiac  nerve. 

On  both  sides  the  middle  cardiac  nerve  (nervus  cardiacus 
medius)  enters  the  thorax  and  is  lost  in  the  deep  cardiac 
plexus.  On  the  right  side  it  passes  behind  or  in  front  of  the 
subclavian  artery ;  on  the  left  side  it  is  continued  downwards 
between  the  common  carotid  and  subclavian  arteries. 

Inferior  Cervical  Ganglion  (ganglion  cervicale  inferius). — 
This  ganglion  is  lodged  in  the  interval  between  the  transverse 
process  of  the  seventh  cervical  vertebra  and  the  neck  of  the 
first  rib.  In  this  position  it  lies  behind  the  vertebral  artery. 
It  is  by  no  means  uncommon  to  find  it  more  or  less  completely 
fused  over  the  neck  of  the  first  rib  with  the  first  thoracic 
ganglion.  Again,  the  connexion  between  it  and  the  middle 
ganglion  is  generally  in  the  form  of  two  or  more  slender  nerve 
cords,  of  which  one  passes  in  front  of  the  subclavian  artery. 
The  loop  which  is  thus  formed  is  termed  the  ansa  Vieussenii 
(ansa  subclavia). 

The  branches  of  the  inferior  cervical  ganglion  are  : — 

1.  Grey  rami  communicantes  to  the  seventh  and  eighth  cervical  nerves. 

2.  Rami  vasculares. 

3.  Inferior  cardiac  nerve. 

The  rami  vasculares  are  fine  branches  which  form  a  plexus 
around  the  subclavian  artery  and  its  branches.  Others, 
remarkable  for  their  large  size,  join  the  vertebral  artery. 

The  lower  cardiac  nerve  (nervus  cardiacus  inferior)  on  both 
sides  enters  the  deep  cardiac  plexus. 

Dissection. — The  little  muscle  termed  the  rectus  capitis  lateralis  should 
now  be  cleaned,  and  its  attachments  defined.  It  lies  in  the  interval 
between  the  transverse  process  of  the  atlas  and  the  occiput,  behind  the 
commencement  of  the  internal  jugular  vein.  The  anterior  division  of  the 
first  cervical  nerve  will  be  seen  emerging  from  under  cover  of  its  inner 
margin. 

VOL.  II — 21 


322  HEAD   AND  NECK 

Eectus  Capitis  Lateralis. — The  rectus  lateralis  arises  from 
the  fore-part  of  the  upper  surface  of  the  extremity  of  the 
transverse  process  of  the  atlas,  and  is  inserted  into  the  under 
surface  of  the  jugular  eminence  of  the  occipital  bone.  It  is 
supplied  by  a  branch  from  the  anterior  division  of  the  first 
cervical  nerve. 

First  Loop  of  the  Cervical  Plexus. — The  anterior  primary 
division  of  the  first  cervical  or  suboccipital  nerve  may  next 
be  examined.  It  will  be  noticed  emerging  from  under  cover 
of  the  inner  surface  of  the  rectus  lateralis  muscle.  It  at  once 
turns  downwards  in  front  of  the  transverse  process  of  the 
atlas,  and,  joining  the  ascending  branch  of  the  second  cervical 
nerve,  forms  the  first  loop  of  the  cervical  plexus.  From  this 
loop  branches  are  given  to  two  muscles — viz.,  the  rectus  capitis 
anticus  major  and  minor.  It  is  likewise  brought  into  con- 
nexion by  means  of  communicating  twigs  with — (i)  the  superior 
cervical  ganglion;  (2)  the  vagus;  (3)  the  hypoglossal. 

If  the  rectus  lateralis  muscle  be  detached  from  the  transverse  process 
of  the  atlas  and  turned  upwards,  a  twig  from  the  anterior  division  of  the 
first  cervical  nerve  will  be  found  entering  its  deep  surface  ;  further,  by 
cutting  through  the  origin  of  the  superior  oblique  muscle  of  the  head,  this 
nerve-division  may  be  traced  to  the  upper  surface  of  the  neural  arch  of  the 
atlas,  where  it  takes  origin  from  the  first  spinal  nerve-trunk  (suboccipital 
nerve). 

The  entire  length  of  the  anterior  primary  division  of  the 
first  cervical  nerve  may  now  be  studied.  It  turns  round  the 
superior  articular  process  of  the  atlas,  under  cover  of  the 
vertebral  artery  and  the  rectus  capitis  lateralis,  and,  gaining 
the  anterior  aspect  of  the  atlas,  it  enters  into  the  formation 
of  the  first  loop  of  the  cervical  plexus.  As  it  lies  in  relation 
to  the  vertebral  artery,  it  is  joined  by  a  filament  from  the 
sympathetic  plexus  which  surrounds  that  vessel. 

Removal  of  the  Head  and  Neck  from  the  Trunk.— By  the  time  that 
the  dissectors  of  the  head  and  neck  have  arrived  at  this  stage  of  their  work, 
the  dissectors  of  the  thorax  have  in  all  probability  finished  their  dissection. 
If  this  be  the  case,  the  head  and  neck  may  be  removed  from  the  trunk  by 
cutting  through  the  vertebral  column  at  the  level  of  the  intervertebral  disc 
between  the  third  and  fourth  dorsal  vertebrae.  By  this  proceeding  the 
three  upper  dorsal  vertebrae,  with  the  attached  portions  of  the  first,  second, 
and  third  pairs  of  ribs,  are  removed  with  the  neck.  The  scalene  muscles 
and  the  longus  colli  are  therefore  preserved  intact. 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA    323 


THE   LATERAL  PART  OF  THE  MIDDLE 
CRANIAL  FOSSA. 

The  structures  contained  within  the  middle  cranial  fossa 
may  now  be  examined,  and,  in  carrying  out  this  dissection, 
the  head  should  be  supported  on  a  block  so  that  the  floor 
of  the  cranial  cavity  looks  upwards.  The  following  are  the 
structures  which  must  be  displayed  : — 

1.  Cavernous  venous  sinus. 

2.  Internal  carotid  artery. 

3.  Middle  meningeal  artery. 

4.  Small  meningeal  artery. 

5.  The   two   roots   of  the    trigeminal    nerve,    with   the    Gasserian 

ganglion    and    the    three    main    divisions    of    the    trigeminal 
nerve. 

6.  Oculo-motor  nerve  (3rd  cranial). 

7.  Trochlear  nerve  (4th  cranial). 

8.  Abducent  nerve  (6th  cranial).  • 

9.  Cavernous  plexus  of  the  sympathetic. 

10.  Great  superficial  petrosal  nerve. 

11.  Small  superficial  petrosal  nerve. 

Dissection.  — To  expose  these  structures,  the  dura  mater  must  be 
stripped  from  the  inner  part  of  the  lateral  portion  of  the  middle  cranial 
fossa.  Enter  the  knife  at  the  anterior  clinoid  process,  and  carry  it 
backwards  to  the  apex  of  the  petrous  bone.  This  incision  must  go  no 
deeper  than  is  necessary  to  divide  the  dura  mater,  and  must  be  made 
immediately  to  the  outer  side  of  the  openings  in  the  membrane  through 
which  the  oculo-motor,  the  trochlear,  and  trigeminal  nerves  pass.  It  is 
very  important  to  preserve  these  apertures  intact,  so  that  the  proximal 
ends  of  these  nerves  may  be  held  in  position  during  the  dissection.  The 
incision  through  the  dura  mater  may  now  be  carried  along  the  upper 
border  of  the  petrous  bone  in  the  line  of  the  superior  petrosal  sinus,  and 
also  outwards  along  the  posterior  margin  of  the  lesser  wing  of  the  sphenoid. 
The  dura  mater  may  now  be  raised,  and  the  greatest  care  must  be  taken 
in  doing  so,  because  it  is  intimately  connected  with  the  nerves  which  lie 
subjacent  to  it.  Thus,  where  it  forms  the  outer  wall  of  the  cavernous 
sinus,  it  is  closely  applied  to  the  oculo-motor  and  trochlear  nerves,  and 
firmly  attached  to  the  ophthalmic  division  of  the  trigeminal  nerve,  whilst 
over  the  petrous  bone  it  is  united  to  the  surface  of  the  Gasserian  ganglion. 
The  edge  of  the  knife,  therefore,  must  be  kept  close  to  the  membrane,  and 
a  small  portion  of  it  may  be  left  upon  the  nerves.  This  can  afterwards  be 
removed  as  the  nerves  are  defined. 

Cavernous  Sinus  (sinus  cavernosus). — The  cavernous  sinus 
has  been  opened  by  the  above  dissection.  It  is  a  short,  wide 
venous  channel,  which  extends  upon  the  side  of  the  body  of 
the  sphenoid  bone,  from  the  lower  and  inner  end  of  the 
sphenoidal    fissure    backwards   to    the    apex    of    the    petrous 


324 


HEAD  AND  NECK 


portion  of  the  temporal  bone.  In  front,  blood  is  conducted 
into  it  by  the  ophthalmic  veins  and  the  sphenoparietal  venous 
sinus  ;  whilst  behind,  the  blood  is  drained  away  by  the  superior 
and  inferior  petrosal  venous  sinuses.  But  it  has  still  other 
connexions ;  thus,  it  receives  some  of  the  inferior  cerebral 
veins,  and  internally  it  is  brought  into  communication  with 
the  corresponding  sinus  of  the  opposite  side  by  means  of  the 
anterior  and  posterior  intercavernous  sinuses  (p.  129).  Lastly, 
one  or  more  emissary  veins  leave  its  under  aspect,  and,  passing 
out  of  the  cranium  by  the  foramen  ovale,  or  it  may  be  through 
the  foramen  Vesalii  when  such  exists  in  the  sphenoid  bone, 
connect  it  with  the  pterygoid  venous  plexus. 

The  cavernous  sinus  is   formed   in   the  same   manner  as 

INT.  CAROTID       INFU_Nb|BULU 

ocuLO-r 

TROC  H 

OPHTHAL 
SUPRAM  AXILLARY 
INFRAMAXILLARY   N 


Fig.   119. — Section  through  the  Cavernous  Sinus.      (After 
Merkel,  somewhat  modified.) 

the  other  venous  sinuses.  The  two  layers  of  the  dura  mater 
are  separated  from  each  other,  and  the  interval  is  lined  by 
a  delicate  membrane.  A  complicated  network  of  interlacing 
trabecular  occupies  the  lumen  of  the  channel,  and  it  is  on 
this  account  that  the  term  "  cavernous "  is  applied  to  it. 
But,  as  we  have  already  indicated,  this  sinus  has  a  special 
importance,  on  account  of  its  being  traversed  by  the  internal 
carotid  artery,  the  cavernous  plexus,  and  the  oculo-motor, 
trochlear,  and  abducent  nerves,  with  the  ophthalmic  division 
of  the  trigeminal  nerve.  The  precise  relation  which  these 
structures  bear  to  its  walls  will  be  described  later  on ;  in  the 
meantime,  it  is  only  necessary  to  state  that  two,  viz.,  the 
internal  carotid  artery  and  the  abducent  nerve,  lie  more 
distinctly  within  the  interval  between  the  two  layers  of  the 
dura  mater  than  the  others.     They  are  shut   out  from   the 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA  325 

blood  channel  by  the  delicate  lining  membrane  of  the  sinus. 
The  oculo-motor  and  trochlear  nerves,  with  the  ophthalmic 
division  of  the  trigeminal  nerve,  are  closely  applied  to  the 
outer  wall  of  the  sinus. 

Trigeminal  or  Fifth  Cranial  Nerve  (nervus  trigeminus). — 
The  two  roots  of  this  nerve  have  already  been  seen  piercing 
the  dura  mater  at  the  apex  of  the  petrous  portion  of  the 
temporal  bone  under  the  anterior  extremity  of  the  tentorium. 
Now  that  the  dura  mater  has  been  raised  from  the  lateral 
part  of  the  middle  cranial  fossa,  the  further  relations  of  these 


Third  nerve 
Fourth  nerve 


Ophthalmic 
nerve 


Sixth  nerve 

Superior 

maxillary 

nerve 

Internal 
carotid 

artery 

Inferior 

maxillary 
nerve 

Sphenoidal 


Infundibulum 
Pituitary  body 


Optic  nerve 

Internal  carotid  artery 

Third  nerve 


Fourth  nerve 

Ophthalmic 

nerve 

Int.  carotid 

artery 
Sixth  nerve 

Superior 

maxillary 

nerve 


rygoid  fossa 


Posterior  nare> 


Vomer 


FlG.  120. — Coronal  section  through  the  Cavernous  Sinus  to  show  the  position 
of  the  Nerves  in  its  wall.  Note  the  branch  given  to  the  pituitary  body 
by  the  internal  carotid  artery. 

nerve-roots  within  the  cranium  may  be  studied.  It  will  be 
noticed  that  the  loosely  connected  and  parallel  funiculi  of 
the  large  sensory  root  (portio  major)  at  once  begin  to  divide 
and  join  with  each  other  so  as  to  form  a  dense  plexiform 
arrangement,  whilst,  at  the  same  time,  the  nerve-root  increases 
somewhat  in  breadth.  The  interlacement  thus  brought  about 
occupies  the  smooth  depression  which  marks  the  anterior 
aspect  of  the  apex  of  the  petrous  portion  of  the  temporal  bone, 
and  it  sinks  into  the  Gasserian  ganglion. 

The  Gasserian  ganglion  (ganglion  semilunare)  is  somewhat 
crescentic  in  form,  and  lies  upon  the  sutural  junction  between 
the  apex   of   the   petrous  bone  and  the  L.rreat   wing   of  the 

n—21  a 


HEAD  AND   NECK 


sphenoid  bone.  Here  it  is  enclosed  within  a  recess  or  space 
formed  by  a  separation  of  the  two  layers  of  the  dura  mater, 
and  called  the  cavum  Meckelii.  The  concavity  of  the  ganglion 
is  directed  inwards,  and  it  is  upon  this  aspect  that  it  receives 
the  interlacing  fibres  of  the  sensory  root  of  the  trigeminal 
nerve ;    the  convexity  of  the  ganglion  is  directed  outwards, 


Levator  palpebral  superioris 
Superior  rectus' 


Superior  oblique 

Lachrymal  gland 


External  rectus 


Sixth  nerve 


Lenticular  ganglion 
Xasal  nerve 


Ophthalmic  division  /  *^« 

of  fifth  nerve  /     ■-  / 

Superior  maxillary  P 

division  of  fifth  nerve  /j 

Motor  root  of 
fifth  nerve 


Trochlea 


Superior  oblique 

ferior  rectus 
Internal  rectus 


Fourth  nerve 


Sixth  nerve 


Optic  nerve 


Gasserian  ganglion 


Third  nerve 


Sixth  nerve 
Fourth  nerve 


Inferior  maxillary  division 
of  fifth  nerve 

FlG.  121. — Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa.      Both 
roots  of  the  fifth  nerve  with  Gasserian  sransflion  are  turned  outwards. 


and  from  it  emerge  the  three  main  divisions  of  the  trigeminal 
nerve.  These  are,  from  before  backwards — (i)  the  first,  or 
ophthalmic  division;  (2)  the  second,  or  superior  maxillary 
division  ;  and  (3)  the  third,  or  inferior  maxillary  division. 
The  outer  surface  of  the  Gasserian  ganglion  has  already  been 
observed  to  be  closely  attached  to  the  deep  surface  of  the 
supporting  or  inner  layer  of  the  dura  mater.  By  its  inner 
part  it  is  connected  with  the  sympathetic  by  some  fine 
filaments  which  come  from  the  carotid  plexus. 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA   327 

The  motor  root  (portio  minor)  of  the  fifth  nerve  should  now 
be  followed.  Before  the  nerve  pierces  the  dura  mater  the 
motor  root  lies  along  the  inner  side  of  the  large  sensory  root, 
but  it  soon  changes  its  position  and  comes  to  lie  upon  the 
under  surface  of  the  sensory  part.  To  display  this  relationship, 
draw  the  cut  ends  of  the  two  roots  through  the  aperture  in  the 
dura  mater  which  leads  into  the  cavum  Meckelii,  and,  gently 
dislodging  the  Gasserian  ganglion  from  its  place,  turn  it 
forwards  and  outwards  so  as  to  expose  its  deep  surface.  The 
small  firm  motor  root  can  readily  be  recognised  lying  in  a 
groove  upon  the  deep  surface  of  the  ganglion ;  and  if  it  be 
raised  from  this,  it  will  be  seen  to  have  no  connexion  with 
the  ganglion,  but  to  be  continued  onwards  towards  the  foramen 
ovale.  It  ultimately  joins  the  inferior  maxillary  division  of 
the  trigeminal  nerve.  This  junction  may  take  place  within 
the  cranium,  in  the  foramen  ovale,  or  immediately  after  it 
gains  the  exterior  of  the  skull  (p.  290). 

The  three  principal  divisions  of  the  trigeminal  nerve  may 
next  be  examined.  Begin  with  the  inferior  maxillary  division, 
which  is  the  largest.  This  proceeds  directly  downwards,  and 
almost  immediately  leaves  the  cranial  cavity  through  the 
foramen  ovale. 

In  isolating  this  large  nerve -trunk  and  defining  the  bony  aperture 
through  which  it  makes  its  exit,  look  carefully  for  the  small  meningeal 
artery  which  enters  the  cranium  through  the  same  foramen.  If  the 
injection  has  been  forced  into  this  vessel  it  can  easily  be  detected.  Through 
the  foramen  ovale  the  minute  emissary  veins  which  connect  the  cavernous 
sinus  with  the  pterygoid  venous  plexus  also  pass. 

The  superior  maxillary  division,  which  is  composed  entirely 
of  sensory  fibres,  is  prolonged  forwards  in  relation  to  the 
lower  part  of  the  cavernous  sinus,  and,  after  a  short  course 
within  the  cranium,  makes  its  exit  through  the  foramen 
rotundum.  Near  its  origin  it  gives  off  a  fine  recurrent  branch 
to  the  dura  mater  of  the  middle  fossa  of  the  cranium. 

The  ophthalmic  division  is  the  smallest  of  the  three  parts  of 
the  trigeminal  nerve,  and,  like  the  supra-maxillary,  it  is  entirely 
composed  of  sensory  fibres.  It  proceeds  forwards  in  the 
outer  wall  of  the  cavernous  sinus,  and  ends  close  to  the 
sphenoidal  fissure  by  dividing  into  three  terminal  branches. 
As  it  traverses  the  sinus  it  is  accompanied  by  the  oculo- 
motor and  trochlear  nerves,  both  of  which  occupy  a  higher 
level.  Like  the  other  two  divisions  of  the  trigeminal  nerve, 
n—21  b 


328  HEAD  AND  NECK 

the   ophthalmic   nerve   gives   off  a   recurrent   branch   to  the 
dura  mater. 

The  terminal  branches  of  the  ophthalmic  division  of  the 
trigeminal  nerve  are  the  nasal,  the  lachrymal,  and  the  frontal. 
The  nasal,  as  a  rule,  takes  origin  first ;  soon  after,  the 
lachrymal  is  given  off,  and  then  the  stem  of  the  nerve  is 
continued  onwards  as  the  frontal  These  three  nerves  enter 
the  orbit  through  the  sphenoidal  fissure. 

Third  or  Oculomotor  Fourth  or  Trochlear,  and  Sixth  or 
Abducent  Nerves. — The  oculo-motor  and  trochlear  nerves,  as 
the  dissector  has  previously  noted,  pierce  the  dura  mater 
within  the  small  triangular  area,  which  is  formed  by  the 
divergence  of  the  attached  and  free  margins  of  the  tentorium. 
They  now  proceed  forwards  in  the  outer  wall  of  the  cavernous 
sinus.  The  third  or  oculo-motor  nerve  occupies  the  highest 
level,  then  comes  the  fourth  or  trochlear  nerve,  and  im- 
mediately below  this  is  the  ophthalmic  division  of  the  fifth  or 
trigeminal  nerve.  They  therefore  present  a  numerical  order 
from  above  downwards.  The  sixth  or  abducent  nerve,  which 
pierces  the  dura  mater  at  the  lower  and  outer  part  of  the 
dorsum  sellae,  will  be  observed  to  wind  round  the  outer  side 
of  the  internal  carotid  artery,  and  then  to  proceed  forwards 
more  directly  within  the  cavernous  sinus  than  the  others  and 
at  a  lower  level  (Fig.  120). 

The  oculo-motor,  trochlear,  and  abducent  nerves  give  off 
no  branches  during  their  course  in  relation  to  the  cavernous 
sinus.  They  all  enter  the  orbit  by  passing  through  the 
sphenoidal  fissure.  Before  doing  so,  the  oculo-motor  nerve 
divides  into  an  upper  and  a  lower  division.  During  their 
passage  through  the  sphenoidal  fissure  the  various  nerves 
undergo  a  change  in  their  relative  positions.  This,  however, 
will  be  studied  in  the  dissection  of  the  orbit  when  that  fissure 
is  opened  up. 

Internal  Carotid  Artery  (arteria  carotis  interna). — The 
intracranial  portion  of  the  internal  carotid  artery  may  now  be 
examined.  It  lies  upon  the  lateral  aspect  of  the  body  of  the 
sphenoid,  and  for  the  greater  part  of  its  course  it  traverses  the 
cavernous  sinus.  It  enters  the  cranium  by  emerging  from  the 
carotid  canal  at  the  apex  of  the  petrous  bone,  and  it  first 
ascends  until  it  reaches  the  root  of  the  posterior  clinoid 
process  ;  here  it  makes  a  bend  and  is  prolonged  forwards  to 
the  lower  root  of  the  anterior  clinoid  process,  where  it  abruptly 


LATERAL  PART  OF  MIDDLE  CRANIAL  FOSSA  329 

turns  upwards  and  pierces  the  dura  mater  immediately  behind 
the  entrance  of  the  optic  nerve  into  the  optic  foramen  and 
on  the  inner  side  of  the  anterior  clinoid  process.  At  this 
point  it  has  been  severed  in  the  removal  of  the  brain,  but  it 
will  be  afterwards  seen  to  end  at  the  commencement  of  the 
Sylvian  fissure  on  the  basal  aspect  of  the  brain,  by  dividing 
into  the  anterior  and  middle  cerebral  arteries.  Throughout 
its  whole  course  it  is  surrounded  by  sympathetic  filaments, 
and  soon  after  its  entrance  into  the  cranium  the  abducent 
nerve  winds  round  its  outer  side. 

The  intracranial  portion  of  the  internal  carotid  artery  gives 
off  the  following  branches  : — 

1.  Branches  to  the  pituitary  body,  j    These  are  minute  twigs 

2.  Branches  to  the  Gasserian  ganglion,  I       which    arise    in    the 

3.  Branches  to  the  dura  mater,  cavernous  sinus. 

4.  Ophthalmic,  ^ 


5.  Posterior  communicating,  \   These  will  be  studied  at  a  later 

6.  Anterior  cerebral,    )    terminal     j       stage. 

7.  Middle  cerebral,      /  branches.  J 


Cavernous  Plexus  (plexus  cavernosus). — The  sympathetic 
filaments  which  form  this  plexus  can  only  be  satisfactorily 
dissected  in  a  subject  which  has  not  been  injected ;  and  even 
then,  the  dissection  is  an  exceedingly  difficult  one.  The 
cavernous  plexus  is  placed  in  the  cavernous  sinus  and  is  chiefly 
massed  upon  the  lower  and  inner  aspect  of  the  internal  carotid 
artery,  at  the  point  where  it  makes  its  bend  upwards.  It 
supplies  filaments  to  the  pituitary  body,  to  the  third  and 
fourth  nerves,  and  to  the  ophthalmic  division  of  the  fifth  or 
trigeminal  nerve,  and  likewise  the  sympathetic  root  to  the 
lenticular  or  ophthalmic  ganglion. 

Great  Superficial  Petrosal  Nerve. — This  minute  nerve, 
along  with  a  small  arterial  twig  from  the  middle  meningeal 
artery,  can  readily  be  exposed  in  the  groove  on  the  anterior 
face  of  the  petrous  bone  which  leads  outwards  to  the  hiatus 
Fallopii.  It  is  placed  under  cover  of  the  Gasserian  ganglion, 
which  must  therefore  be  turned  forwards  and  outwards. 
Entering  the  hiatus  Fallopii,  the  great  superficial  petrosal 
nerve  is  conducted  to  the  aqueduct  of  Fallopius,  where  it 
joins  the  geniculate  ganglion  of  the  facial  nerve.  If  traced 
in  the  opposite  direction,  it  will  be  found  at  the  posterior 
aspect  of  the  body  of  the  sphenoid  bone  to  join  the  large 
deep  petrosal    nerve    from    the    carotid     plexus.     The    trunk 


330  HEAD  AND  NECK 

formed   by  the   union   of  these   two  filaments  is  the    Vidian 
nerve. 

The  Small  Superficial  Petrosal  Nerve  appears  upon  the  anterior  face 
of  the  petrous  bone  through  an  aperture  which  is  placed  immediately 
external  to  the  hiatus  Fallopii.  It  leaves  the  cranial  cavity  by  passing 
downwards  between  the  great  wing  of  the  sphenoid,  and  the  petrous  part 
of  the  temporal  bone,  to  reach  the  otic  ganglion.  This  minute  nerve,  as 
has  already  been  mentioned  (p.  314),  is  formed  by  the  union  of  the  tympanic 
branch  of  the  glosso-pharyngeal  with  a  branch  from  the  geniculate  ganglion 
of  the  facial. 

External  Superficial  Petrosal  Nerve. — It  is  convenient  at  this  stage  to 
take  note  of  a  fourth  petrosal  nerve — the  external  superficial  petrosal.  It 
takes  origin  from  the  sympathetic  plexus,  which  accompanies  the  middle 
meningeal  artery,  and,  entering  the  petrous  bone,  is  conducted  to  the 
geniculate  ganglion  of  the  facial  nerve. 

Middle  and  Small  Meningeal  Arteries. — The  entrance  of 
the  middle  meningeal  artery  through  the  foramen  spinosum 
should  now  be  examined.  It  gives  minute  twigs  to  the 
Gasserian  ganglion,  and  one — the  petrosal  artery — which 
accompanies  the  great  superficial  petrosal  nerve  into  the 
hiatus  Fallopii.  The  further  course  of  the  middle  meningeal 
artery  has  already  been  described  (pp.  130  and  290).  The 
small  recurrent  branch  of  the  inferior  maxillary  division  of 
the  fifth  nerve  also  enters  the  cranium  through  the  foramen 
spinosum  (p.  290). 

The  small  meningeal  artery  enters  the  cranium  through 
the  foramen  ovale,  and  is  chiefly  distributed  to  the  Gasserian 
ganglion. 


DISSECTION  OF  THE  ORBIT. 

Within    the   orbital   cavity   we   find   grouped   around    the 
eyeball  and  the  optic  nerve  the  following  structures : — 

'Rectus  superior. 

Rectus  inferior. 

Rectus  externus. 

Rectus  internus. 

Obliquus  superior. 

Obliquus  inferior. 
^Levator  palpebrce  superior. 


Muscles, 


T  Ophthalmic  artery  and  its  branches. 
.  \  Ophthalmic  veins  (superior  and  inferic 


Vessels,     .     .  <  Ophthalmic  veins  (superior  and  inferior)  with  their  tribu- 
[         taries. 


DISSECTION   OF  THE  ORBIT  331 

'Oculo-motor  (3rd  cranial). 
Trochlear  (4th  cranial). 
Abducent  (6th  cranial). 

Nerves,     .     .-'  |ro^ta1'  |  from  ophthalmic  division  of  the  trigeminal 

Lachrymal,       -  or  fifth  cranial  nerve- 

ISasal,  J 

Orbital  branch  of  the  superior  maxillary  division  of  the 

trigeminal  or  fifth  cranial  nerve. 

Lenticular  ganglion. 

Lachrymal  gland. 

The  capsule  of  Tenon. 

Dissection. — The  roof  of  the  orbit  must  be  removed.  The  greater  part 
of  this  dissection  should  be  done  with  a  sharp  chisel.  Begin  by  removing 
the  thick  cranial  wall  above  the  orbital  opening,  leaving  only  a  thin 
portion  corresponding  to  the  superior  orbital  arch.  Whilst  this  is  being 
done,  care  should  be  taken  to  preserve  the  soft  parts  of  the  forehead  and 
the  upper  eyelid.  It  is  of  great  advantage  to  retain  throughout  the  whole 
examination  of  the  orbital  cavity  the  bony  ring  which  constitutes  its  opening 
on  the  face.  The  thin  roof  of  the  orbit  may  next  be  removed  with  the 
chisel.  The  lesser  wing  of  the  sphenoid,  where  it  forms  the  upper  boundary 
of  the  sphenoidal  fissure,  should  be  taken  away  by  the  bone  pliers,  but  the 
dissector  should  carefully  preserve  intact  the  ring  of  bone  around  the  optic 
foramen.  The  sphenoidal  fissure  is  now  fully  opened  up,  and  the  various 
nerves,  as  they  enter  the  orbit  from  the  cavernous  sinus,  may  be  followed 
out.  Lastly,  the  anterior  clinoid  process  may  be  taken  away  with 
advantage. 

Periosteum. — If  the  above  dissection  has  been  successfully 
carried  out,  the  periosteum  clothing  the  under  surface  of  the 
orbital  roof  will  be  exposed  uninjured.  The  periosteum  of 
the  orbit  forms  a  funnel-shaped  sheath,  which  encloses  all  the 
contents  of  the  cavity,  and  is  but  loosely  attached  to  its  bony 
walls.  Behind,  it  will  be  observed  to  be  directly  continuous 
through  the  sphenoidal  fissure  with  the  dura  mater.  Expand- 
ing with  the  cavity,  it  becomes  continuous  in  front  around 
the  orbital  opening  with  the  periosteum,  which  clothes  the 
exterior  of  the  skull.  Here  also  it  presents  important  con- 
nexions with  the  palpebral  ligaments  (p.  273). 

Reflection  of  the  Periosteum  and  the  subsequent  Dissection. — The 

periosteum  should  be  divided  along  the  middle  line  of  the  orbit,  and  then 
transversely  close  to  the  orbital  opening.  It  can  now  be  thrown  inwards 
and  outwards.  When  this  is  done,  the  lachrymal  gland  will  be  exposed  in 
the  fore  and  outer  part  of  the  cavity  resting  upon  the  upper  and  outer 
aspect  of  the  eyeball.  Further,  the  large  frontal  nerve,  lying  upon  the 
upper  surface  of  the  levator  palpebrse  superioris,  will  be  seen  stretching 
forwards  in  the  middle  line  of  the  orbit  ;  as  it  approaches  the  fore-part  <>l 
the  cavity,  it  is  joined  by  the  supra-orbital  artery.  The  other  superficial 
structures  are  usually  more  or  less  obscured  by  the  soft  pliable  fat,  which 
everywhere  tills  up  the  interstices  between  the  different  orbital  contents. 
On  carefully  separating  this,  along  the  inner  wall  of  the  orbit,  the  superior 


HEAD  AND  NECK 


oblique  muscle  will  be  more  fully  displayed,  and  lying  upon  and  entering 
the  hinder  part  of  this  muscle  the  small  trochlear  or  fourth  cranial  nerve 
will  be  discovered.  As  a  general  rule  the  dissector  fails  to  find  this  nerve, 
because  he  looks  for  it  too  far  forwards.  Lastly,  the  lachrymal  nerve  and 
artery  will  be  found  running  along  the  outer  wall  of  the  orbit,  above  the 
level  of  the  upper  margin  of  the  external  rectus  muscle. 

These  structures  must  be  thoroughly  cleaned  and  isolated  by  the  removal 
of  the  fat  from  around  them.  In  tracing  the  superior  oblique  muscle 
forwards,  it  will  be  found  to  end  in  a  slender  tendon,  which  passes  through 


Lachrymal  gland 


Frontal  nerve 


Short  ciliary  nerves 
Lachrymal  nerve' 


Infra-trochlear  nerve 
-Supra-trochlear  nerve 
Supra-orbital  nerve 

j    Nasal  nerve  proper 

Long  ciliary  nerves 

Nasal  nerve 
Ophthalmic  ganglion 


\    --VOptie  nerve 

Ophthalmic  nerve- 
Superior  maxillary  nerve 

--  Motor  root  of  trigeminal 

•Inferior  maxillary  nerve 

*xGasserian  ganglion  (thrown  outwards) 
Fig.   122. — The  Ophthalmic  Nerve  of  the  Left  Side. 

a  ringdike  pulley,  attached  to  the  frontal  bone  at  the  inner  angle  of  the 
orbit.  This  pulley  must  be  defined,  and  the  tendon  of  the  muscle  followed 
onwards  to  its  insertion  into  the  eyeball.  It  will  be  observed  that  the 
levator  palpebral  superioris  lies  upon  the  upper  surface  of  the  superior 
rectus,  and  if  it  be  raised,  a  nerve  twig  will  be  noticed  emerging  from  the 
substance  of  the  rectus  superior  for  the  supply  of  the  levator  palpebral 
muscle.     This  is  a  branch  of  the  superior  division  of  the  third  nerve. 

The  dissection  of  the  above  parts  will  be  facilitated  by  grasping  the 
front  of  the  eyeball  with  the  forceps  and  drawing  it  forwards.  It  may 
be  retained  in  this  position  by  running  a  fine  needle  and  thread  through 
the  ocular  conjunctiva  and  stitching  it  to  the  nose.  In  doing  this,  however, 
take  care  that  the  needle  does  not  penetrate  the  cornea,  because  this  might 
render  the  subsequent  inflation  of  the  eyeball  impossible. 


DISSECTION  OF  THE  ORBIT  333 

Frontal  Nerve  (nervus  frontalis). — The  frontal  nerve  is 
the  continuation  of  the  stem  of  the  ophthalmic  division  of 
the  trigeminal  or  fifth  nerve,  after  it  has  given  off  its  lachry- 
mal and  nasal  branches.  It  enters  through  the  sphenoidal 
fissure  above  the  muscles,  and  proceeds  forwards  upon  the 
upper  surface  of  the  levator  palpebral  superioris  immediately 
subjacent  to  the  periosteal  lining  of  the  orbital  cavity.  At  a 
variable  distance  from  the  orbital  opening,  it  ends  by  dividing 
into  the  supra-orbital  and  supra-trochlear  nerves. 

The  supra-trochlear  nerve  is  the  inner  and  smaller  of  the 
two  terminal  branches  of  the  frontal.  It  runs  towards  the 
pulley  of  the  superior  oblique  muscle,  above  which  it  leaves 
the  orbit,  by  turning  round  the  orbital  arch  to  reach  the 
forehead.  Its  further  course  has  already  been  described 
(pp.  107  and  265).  In  the  orbit  it  gives  off  one  small  twig 
close  to  the  pulley  of  the  superior  oblique  muscle.  This 
passes  downwards  to  join  the  infra- trochlear  branch  of  the 
nasal  nerve. 

The  supra-orbital  nerve  is  continued  forward  in  the  line 
of  the  parent  stem,  and,  passing  through  the  supra-orbital 
notch  or  foramen,  it  turns  upwards  on  the  forehead  (pp.  109 
and  265).  In  the  dissection  of  the  scalp  this  nerve  has  been 
seen  to  divide  into  an  outer  and  inner  division.  Sometimes 
this  division  takes  place  within  the  orbit,  and  in  that  case  the 
outer  larger  part  occupies  the  supra-orbital  notch. 

Lachrymal  Nerve  (nervus  lacrimalis). — This  is  the  smallest 
of  the  terminal  branches  of  the  ophthalmic  division  of  the 
fifth.  It  enters  the  orbit  through  the  sphenoidal  fissure 
above  the  level  of  the  muscles,  and  proceeds  forwards  along 
the  outer  wall  of  the  cavity,  and  above  the  upper  margin 
of  the  external  rectus  muscle.  At  the  fore-part  of  the  orbit 
it  continues  its  course  under  cover  of  the  lachrymal  gland 
until  it  reaches  the  outer  part  of  the  upper  eyelid,  in  which 
it  ends  (p.  265).  Within  the  orbital  cavity  it  gives  numerous 
twigs  to  the  deep  surface  of  the  lachrymal  gland,  and  sends 
downwards  a  filament  which  connects  it  with  the  orbital 
branch  of  the  superior  maxillary  nerve. 

Fourth  Cranial  Nerve  (nervus  trochlearis). — This  small 
nerve  is  destined  entirely  for  the  supply  of  the  superior 
oblique  muscle.  Entering  the  orbit  through  the  sphenoidal 
fissure  above  the  muscles,  it  is  continued  forwards  and  inwards 
under   the   periosteum.     It   finally   sinks   into   the   upper   or 


334  HEAD  AND  NECK 

orbital  surface  of  the  superior  oblique  muscle  not  far  from 
its  origin. 

Lachrymal  Gland. — The  lachrymal  gland  is  a  small  flattened 
body  of  an  oval  form,  and  distinctly  lobular  structure,  which 
is  placed  obliquely  in  the  fore  and  outer  part  of  the  orbital 
cavity.  It  consists  of  two  parts  or  groups  of  lobules — an 
orbital  and  a  palpebral — imperfectly  separated  from  each  other. 
The  orbital  part  (glandula  lacrimalis  superior)  constitutes  the 
main  mass  of  the  gland.  Its  outer  surface  is  convex,  and  is 
lodged  in  a  hollow  upon  the  inner  aspect  of  the  external 
angular  process  of  the  frontal  bone.  It  is  bound  to  the  outer 
part  of  the  orbital  arch  by  short  fibrous  bands  which  proceed 
from  the  periosteum.  The  deep  or  inner  surface  is  slightly 
concave,  and  rests  upon  the  levator  palpebral  superioris  and 
external  rectus,  which  intervene  between  it  and  the  eyeball. 
The  small  palpebral  lobe  (glandula  lacrimalis  inferior)  is  placed 
in  front  of  the  orbital  part,  from  which  it  is  partially  separated 
by  the  expanded  tendon  of  the  levator  palpebral  superioris. 
It  projects  into  the  back  part  of  the  upper  eyelid,  and  rests 
upon  the  conjunctiva  which  lines  the  under  aspect  of  the  lid. 
This  portion  of  the  gland  has  been  already  examined  in  the 
dissection  of  the  eyelids  (p.  276) ;  but  even  in  the  undissected 
subject  it  can  be  seen  through  the  conjunctiva  if  the  upper 
eyelid  be  fully  everted. 

The  lachrymal  gland  secretes  the  tears,  and  its  ducts 
(three  to  five  from  the  orbital  part  and  three  to  nine  from 
the  palpebral  part)  open  upon  the  under  surface  of  the  upper 
eyelid  in  the  neighbourhood  of  the  fornix  (p.  277). 

Levator  Palpebral  Superioris. — This  muscle  rests  upon  the 
upper  surface  of  the  rectus  superior.  Behind,  it  is  narrow 
and  pointed,  but  it  expands  as  it  passes  forwards  above  the 
eyeball  to  reach  the  upper  eyelid.  It  arises  from  the  under 
surface  of  the  roof  of  the  orbit  immediately  in  front  of  the 
optic  foramen,  and  in  the  fore-part  of  the  orbital  cavity  it 
widens  out  into  a  broad  membranous  expansion,  the  con- 
nexions of  which  have  already  been  described  (p.  276).  The 
outer  and  inner  margins  of  this  expansion  are  fixed  to  the  rim 
of  the  orbital  opening,  in  close  proximity  to  the  external  and 
internal  tarsal  ligaments.  By  these  attachments  excessive  action 
of  the  muscle  upon  the  upper  eyelid  is  in  a  measure  checked. 

Dissection. — The  frontal  nerve  should  be  divided,  and  the  ends  thrown 
forwards  and  backwards.     The  levator  palpebne  superioris  may  also  be 


DISSECTION  OF  THE  ORBIT 


cut  midway  between  its  origin  and  insertion.  On  raising  the  posterior 
portion  a  minute  nerve  twig  will  be  observed  entering  its  deep  or  ocular 
surface.  This  comes  from  the  superior  division  of  the  third  or  oculo-motor 
nerve. 

The  eyeball  should  now  be  inflated.  This  may  be  done  from  the 
front  or  from  behind.  If  the  latter  method  is  selected,  gently  separate 
the  fat  under  cover  of  the  superior  rectus  muscle,  and,  pushing  aside  the 
ciliary  nerves  and  vessels  from  the  optic  nerve,  place  a  ligature  around  it 
close  to  the  eyeball.  A  minute  aperture  should  next  be  made  in  the  sheath 
of  the  nerve  behind  the  ligature,  and,  introducing  a  blow-pipe  into  this, 
thrust  it  forcibly  forwards  into  the  interior  of  the  eyeball.  The  pipe  should 
be  provided  with  a  stylette  so  as  to  keep  the  aperture  free.  When  the 
globe  of  the  eye  is  fully  inflated,  the  ligature  may  be  tightened  as  the  blow- 
pipe is  withdrawn.  A  very  much  better  plan,  however,  is  to  inflate  the 
eyeball  from  the  front.  For  this  purpose  an  oblique  valvular  aperture  is 
made  in  an  inward  direction 
through  the  sclero-corneal  junc- 
tion, with  the  point  of  a  sharp 
narrow -bladed  knife.  Through 
this  the  blow-pipe  may  be  intro- 
duced, and  on  its  withdrawal  after 
the  inflation  of  the  eyeball  the 
valvular  character  of  the  opening 
is  sufficient  to  prevent  the  escape 
of  the  air. 

At  the  back  of  the  eyeball  the 
dissector  will  notice  a  quantity  of 
loose  bursal- like  tissue.  This  is 
the  Capsule  of  Tenon.  Seize  the 
upper  part  of  this  with  the  forceps, 
and  remove  a  small  portion  with 
a  pair  of  scissors.  An  aperture 
is  thus  made  into  the  capsule,  and 
the  handle  of  the  knife  can  be 
introduced  into  the  space  between 
it  and  the  eyeball.  In  favourable 
cases  the  extent  of  the  capsule  can 
be  gauged,  and  perhaps  even  the 
prolongations  or  sheaths  which  it  gives  to  the  tendons  of  the  ocular  muscles 
made  out.     The  description  of  the  capsule  of  Tenon  is  given  on  p.  345. 

Rectus  Superior. — The  rectus  superior,  which  lies  under 
cover  of  the  levator  palpebrae  superioris,  is  now  fully  exposed. 
It  arises  from  the  upper  margin  of  the  optic  foramen,  and, 
passing  forwards  above  the  optic  nerve,  ends  upon  the  upper 
aspect  of  the  eyeball  in  a  thin,  delicate  tendon,  which  expands 
somewhat  to  be  inserted  into  the  sclerotic  coat  about  three  or 
four  lines  behind  the  sclero-corneal  junction.  It  is  supplied  by 
a  branch  from  the  superior  division  of  the  oculo-motor  nerve. 

Superior  Oblique  Muscle  (musculus  obliquus  superior). — 
This  muscle  arises  from  the  roof  of  the  orbit  immediately  in 
front  of  the  upper  and  inner  part  of  the  optic  foramen,   and 


Fig.  123. 
Oblique 
Meyer. ) 


-  Diagram    of    the    Superior 
Muscle.       (From    Hermann 


a.  Pulley  and  synovial  sheath. 


336  HEAD  AND  NECK 

extends  forwards  along  the  inner  wall  of  the  cavity  above  the 
internal  rectus.  At  the  fore-part  of  the  orbit  it  ends  in  a 
slender  tendon,  which  enters  the  pulley  and  at  once  changes 
its  direction.  It  now  proceeds  outwards  and  slightly  back- 
wards upon  the  upper  surface  of  the  eyeball,  and  under  cover 
of  the  superior  rectus.  Beyond  the  outer  edge  of  the  latter 
muscle  the  tendon  expands  somewhat,  and  is  inserted  into 
the  sclerotic  coat  midway  between  the  entrance  of  the  optic 
nerve  and  the  cornea. 

The  pulley  through  which  the  tendon  passes  is  a  small 
fibro-cartilaginous  ring,  which  is  attached  by  fibrous  tissue 
to  the  trochlear  fossa — a  depression  in  the  frontal  bone  close 
to  the  internal  angular  process.  The  pulley  is  lined  by  a 
small  synovial  sheath  which  facilitates  the  movement  of  the 
tendon  within  it,  and  from  its  outer  margin  it  gives  a  fibrous 
investment  to  the  tendon. 

Dissection. — The  superior  rectus  muscle  should  now  be  divided  midway 
between  its  origin  and  its  insertion,  and  the  cut  ends  thrown  backwards 
and  forwards.  On  raising  the  posterior  part  of  the  muscle  the  superior 
division  of  the  third  nerve  is  brought  into  view,  and  will  be  seen  to  sink 
into  its  deep  or  ocular  surface,  and  at  the  same  time  send  a  twig  to  the 
levator  palpebrae  superioris.  The  removal  of  some  fat  will  bring  the  optic 
nerve  more  fully  into  view.  At  the  back  part  of  the  orbit  three  structures 
will  be  observed  crossing  the  optic  nerve — viz.,  (i)  the  nasal  nerve  ;  (2)  the 
ophthalmic  artery  ;  and  (3)  the  superior  ophthalmic  vein.  These  should 
be  carefully  cleaned  and  their  branches  followed  out.  From  the  nasal 
nerve,  one  or  two  delicate  thread-like  branches — the  long  ciliary  nerves — 
will  be  found  passing  forwards  along  the  optic  nerve  to  reach  the  eyeball. 
The  short  ciliary  nerves,  much  more  numerous,  accompany  the  long  ciliary 
branches,  and  can  readily  be  disengaged  from  the  fat  which  surrounds  the 
optic  nerve.  A  strong  member  of  this  group  should  be  selected  and 
followed  backwards  ;  it  will  lead  the  dissector  to  the  lenticular  or 
ophthahnic  ganglion.  This  is  a  minute  body  which  is -situated  upon  the 
outer  side  of  the  optic  nerve  far  back  in  the  orbit.  With  a  little  patience 
and  care  the  roots  which  the  nasal  nerve  and  inferior  division  of  the  oculo- 
motor or  third  nerve  give  to  this  ganglion  can  be  isolated,  and  perhaps  even 
the  sympathetic  root  from  the  cavernous  plexus  may  be  found. 

Optic  Nerve  (nervus  opticus). — The  optic  nerve  enters  the 
orbit  through  the  optic  foramen.  It  carries  with  it  a  strong 
loose  sheath  of  dura  mater,  and  also  a  more  delicate  invest- 
ment from  the  arachnoid.  The  ophthalmic  artery  which 
accompanies  it  lies  in  relation  to  its  outer  and  lower  aspect. 
Within  the  orbit  the  nerve  inclines  forwards  and  outwards, 
and  at  the  same  time  somewhat  downwards,  and,  gaining 
the  back  of  the  eyeball,  it  pierces  the  sclerotic  coat  a  short 
distance  to  the  inner  side  of  its  centre.     As  the  dissector  has 


DISSECTION  OF  THE  ORBIT  337 

already  observed,  its  upper  surface  is  crossed  by  the  ophthalmic 
artery  and  vein  and  the  nasal  nerve,  and  it  is  closely 
accompanied  by  the  delicate  ciliary  nerves  and  vessels.  The 
optic  nerve  is  slightly  longer  than  the  distance  which  it  has  to 
run  from  the  optic  foramen  to  the  globe  of  the  eye,  so  that  the 
movements  of  the  eyeball  may  not  be  interfered  with.  Within 
the  eyeball  the  optic  nerve  spreads  out  in  the  retina. 

Nasal  Nerve  (nervus  naso-ciliaris). — The  nasal  nerve  arises 
in  the  fore-part  of  the  cavernous  sinus  from  the  ophthalmic 
division  of  the  trigeminal.  It  passes  through  the  sphenoidal 
fissure  and  enters  the  orbital  cavity  between  the  two  heads  of 
the  external  rectus  muscle,  and  between  the  two  divisions  of 
the  third  nerve.  It  now  inclines  forwards  and  inwards,  and, 
crossing  the  optic  nerve  obliquely,  it  runs  between  the  internal 
rectus  and  superior  oblique  muscles.  Here  it  reaches  the 
inner  wall  of  the  orbit,  and  ends  by  dividing  into  two  terminal 
branches — viz.,  the  infra-trochlear  and  the  nasal  proper.  In  ad- 
dition to  these  it  gives  off  in  the  orbit  the  following  branches: — 

1.  Long  root  to  the  lenticular  ganglion. 

2.  Long  ciliary  nerves. 

The  long  ganglionic  root  (radix  longa  ganglii  ciliaris)  is  a 
very  slender  filament  which  springs  from  the  nasal  as  it  enters 
the  orbit  between  the  heads  of  the  external  rectus.  It  proceeds 
forwards  on  the  outer  side  of  the  optic  nerve,  and  enters  the 
upper  and  back  part  of  the  lenticular  ganglion. 

The  long  ciliary  nerves  (nervi  ciliares  longi) — usually  two 
in  number — spring  from  the  nasal  as  it  crosses  the  optic 
nerve.  They  proceed  forwards  upon  the  inner  side  of  the 
optic  nerve  to  reach  the  globe  of  the  eye,  where  they  pierce 
the  sclerotic.  One  of  the  long  ciliary  nerves  very  constantly 
unites  with  one  of  the  short  ciliary  filaments. 

The  infra-trochlear  ?ierve  runs  forwards  along  the  inner  wall 
of  the  orbit  under  cover  of  the  superior  oblique  muscle. 
Passing  under  the  trochlea  of  that  muscle,  it  emerges  from 
the  orbit  and  appears  upon  the  face,  where  it  has  already 
been  dissected  (p.  265).  Near  the  pulley  it  receives  a 
communicating  twig  from  the  supra-trochlear  nerve. 

The  nasal  proper  is  the  larger  of  the  two  terminal  branches 
of  the  nasal  nerve.  It  leaves  the  orbit  by  the  anterior  internal 
orbital  canal,  and  is  conducted  to  the  interior  of  the  cranium, 
in  which  it  appears  at  the  outer  margin  of  the  cribriform  plate 
of  the  ethmoid.      The  canal  in  which  it  runs  can  readily  be 

VOL.  II — 22 


33%  HEAD  ANT)  NECK 

opened  up  by  the  bone  pliers  and  the  nerve  exposed  within  it. 
Upon  the  cribriform  plate  it  turns  forwards  under  the  dura 
mater,  and  almost  immediately  disappears  through  a  slit-like 
aperture  at  the  side  of  the  crista  galli,  to  reach  the  nasal 
cavity.  Here  it  gives  branches  to  the  mucous  membrane, 
and  is  continued  downwards  upon  the  posterior  aspect  of  the 
nasal  bone.  Finally,  it  emerges  upon  the  face  by  passing 
between  the  lower  margin  of  the  nasal  bone  and  the  upper 
lateral  cartilage  of  the  nose.  Its  terminal  filaments  have 
already  been  described  (p.  265). 

The  nasal  nerve  proper,  therefore,  takes  a  most  circuitous 
route,  being  found — (1)  in  the  orbit  ;  (2)  in  the  cranium  : 
(3)  in  the  nasal  fossa ;  and  (4)  in  the  face. 

Lenticular  Ganglion  (ganglion  ciliare) — (Fig.  122). — The 
lenticular  ganglion  is  a  minute  quadrangular  body,  not  much 
larger  than  the  head  of  a  large  pin ;  but  its  size  varies 
considerably  in  different  subjects.  It  is  placed  in  the  back 
part  of  the  orbit  between  the  optic  nerve  and  the  external 
rectus  muscle,  and  very  commonly  on  the  outer  side  of  the 
ophthalmic  artery.  By  its  posterior  border  it  receives  its 
three  roots ;  whilst  from  its  anterior  border  the  short  ciliary 
nerves  are  given  off. 

The  sensory  root  comes  from  the  nasal,  and  is  called  the 
long  root.  It  enters  the  upper  and  hinder  angle  of  the 
ganglion.  The  short  or  motor  root  is  a  short,  stout  trunk  ;  it 
comes  from  the  branch  of  the  oculo-motor  nerve,  which  goes 
to  the  inferior  oblique  muscle,  and  it  enters  the  lower  and 
hinder  angle  of  the  ganglion.  The  sympathetic  root  comes 
from  the  cavernous  plexus,  and  joins  the  posterior  border  of 
the  ganglion,  close  to  the  entrance  of  the  long  root  from  the 
nasal  nerve.  In  some  cases  it  joins  the  long  root  before  it 
reaches  the  ganglion. 

The  short  ciliary  nerves  (nervi  ciliares  breves)  are  from  four 
to  six  in  number,  and  they  come  off  in  two  groups,  of  which 
one  emerges  from  the  upper  and  fore  angle  of  the  ganglion, 
whilst  the  other  springs  from  its  lower  and  fore  angle.  The 
lower  group  is  generally  more  numerous  than  the  upper.  As 
these  fine  nerves  proceed  along  the  optic  nerve  they  divide, 
and  thus  increase  in  number ;  at  the  back  of  the  eyeball  from 
twelve  to  eighteen  may  be  counted.  Finally  they  pierce  the 
sclerotic  by  a  series  of  apertures  which  are  placed  around  the 
entrance  of  the  optic  nerve. 


DISSECTION  OF  THE  ORBIT 


339 


Ophthalmic  Artery  (arteria  ophthalmica). — The  ophthalmic 
artery  is  a  branch  of  the  internal  carotid,  and  it  accompanies 
the  optic  nerve  into  the  orbit  through  the  optic  foramen.  At 
first  it  lies  below  the  optic  nerve,  but  it  soon  winds  round  the 
outer  side  of  the  nerve,  and  crossing  it  superficially  proceeds 
forwards  along  the  inner  wall  of  the  orbit,  under  cover  of  the 
superior  oblique  muscle.  At  the  inner  angle  of  the  orbit  it 
ends  by  dividing  into  two  terminal  branches — viz.,  the  frontal 
and  the  nasal  (Fig.  125). 

The  branches  of  the  ophthalmic  artery  are  very  numerous, 

-Cc 


Canal  of  Schlemm 

Anterior  ciliary    — 
artery 


Sclerotic  coat 


Vena  vorticosa 


Long  posterior 
ciliary  artery 


Anterior  ciliary 
artery 

Ciliary  muscle 


Long  posterior 
ciliary  artery 

Vena  vorticosa 


Fig.  124. 


Long  posterior 
ciliary  artery 

-Dissection  of  the  Eyeball  showing  the  Distribution 
of  the  Ciliary  Nerves  and  Vessels. 


and  they  can  seldom  be  satisfactorily  displayed,  unless  a 
special  injection  has  been  made,  or  a  cold  injection  used. 
They  are : — 

7- 


Ciliary. 

Supra-orbital. 

Ethmoidal. 


Palpebral. 

8.  Nasal. 

9.  Frontal. 


1.  The  lachrymal. 

2.  Muscular. 

3.  Arteria  retina.-  centralis. 

The  lachry?nal  artery  (arteria  lacrimalis)  accompanies  the 
lachrymal  nerve,  and  supplies  the  gland  of  that  name  and  the 
conjunctiva.  Two  branches,  named  external  palpebral  (aiterizc 
palpebrales  laterales),  form  an  arch  (arcus  tarseus)  in  each  eye- 
lid, near  the  free  margin,  with  the  internal  palpebral  arteries. 

The  muscular  twigs  (rami  musculares)  come  off  at  variable 
points,  not  only  from  the  main  artery,  but  also  from  certain 
of  its   branches.      They  supply  the  muscles  contained  in  the 
orbital  cavity. 
[l — 22  a 


34° 


HEAD  AND  NECK 


The  arteria  retince  centralis  is  a  minute  but  important 
artery.  It  pierces  the  inner  and  under  aspect  of  the  optic 
nerve  about  half  an  inch  behind  the  eyeball,  and  is  conducted 
in  its  substance  to  the  interior  of  the  globe  of  the  eye. 

The  ciliary  arteries  are  very  numerous.  Two  groups  are 
recognised — viz.,  a  posterior  and  an  anterior.  The  posterior 
ciliary  arteries  run   with   the   ciliary  nerves.      They  arise  by 


Internal  palpebt 
Nasal 
Frontal — 


Infra-orbital  nerve 

Anterior  ethmoidal 
and  nasal  nerve 


Ciliary 
Posterior  ethmoidal  — 
Ophthalmic 


External 
palpebral 


Supra-orbital 


Arteria  retina; 
centralis 


Ciliary 

Muscular 

Lachrymal 


Ophthalmic 

"Nasal  nerve 

-Internal  carotid 

Fig.  125. — Diagram  of  the  Ophthalmic  Artery  and  its  Branches. 
(After  Quain  and  Meyer,  modified. ) 

two  trunks  which  spring  from  the  ophthalmic  whilst  it  lies 
below  the  optic  nerve.  These  divide  into  several  slender 
branches,  which  pierce  the  sclerotic  around  the  entrance 
of  the  optic  nerve.  Two  members  of  this  group  of  vessels 
enter  the  eyeball  on  either  side  of  the  optic  nerve,  somewhat 
apart  from  the  others.  They  are  termed  the  long  ciliary 
arteries  (arterise  ciliares  posteriores  longae)  (Fig.  124).  The 
anterior  ciliary  arteries  (arterise  ciliares  anteriores)  come  off  in 
the  fore-part  of  the  orbit  from  the  lachrymal  and  muscular 
branches.       They   vary  in    number   from   six   to    eight,    and 


DISSECTION  OF  THE  ORBIT  341 

run  to  the  anterior  part  of  the  eyeball,  where  they  form  an 
arterial  circle  under  the  conjunctiva.  Finally,  they  pierce 
the  sclerotic  immediately  behind  the  cornea. 

The  supra-orbital  artery  (arteria  supraorbitalis)  accom- 
panies the  supra -orbital  nerve,  and  thus  gains  the  forehead, 
where  it  has  been  dissected  at  a  previous  stage  (p.  in ). 

The  ethmoidal  arteries  are  two  in  number — anterior  and 
posterior — and  they  run  to  the  anterior  and  posterior  internal 
orbital  foramina  on  the  inner  wall  of  the  orbit.  The  posterior 
ethmoidal  artery  (arteria  ethmoidalis  posterior)  supplies  the 
mucous  lining  of  the  posterior  ethmoidal  cells,  and  sends 
twigs  to  the  upper  part  of  the  nose.  The  anterior  ethmoidal 
artery  (arteria  ethmoidalis  anterior)  is  a  larger  branch.  It 
runs  in  company  with  the  nasal  nerve  proper,  and  gives  off 
minute  twigs  at  each  stage  of  its  course.  Thus  in  the 
anterior  internal  orbital  canal  it  gives  branches  to  the  mucous 
lining  of  the  anterior  ethmoidal  cells  and  the  frontal  sinus  ; 
during  its  short  sojourn  in  the  cranial  cavity  it  supplies  the 
small  anterior  meningeal  artery  (arteria  meningea  anterior) 
(p.  130);  in  the  nasal  cavity  it  gives  twigs  to  the  mucous 
membrane ;  whilst  its  terminal  branch  appears  on  the  face  to 
supply  parts  on  the  side  of  the  nose. 

The  internal  palpebral  branches  (arteria  palpebrals  medi- 
ates) come  off  near  the  orbital  opening,  and  are  two  in 
number — one  for  the  upper  and  the  other  for  the  lower  eye- 
lid (p.  276). 

The  nasal  branch  (arteria  dcrsalis  nasi)  is  distributed  at 
the  root  of  the  nose,  and  anastomoses  with  the  angular 
branch  of  the  facial  artery. 

The  frontal  artery  (arteria  frontalis)  accompanies  the 
supra-trochlear  nerve  to  the  forehead,  where  it  has  already 
been  dissected  (p.  in). 

Ophthalmic  Veins. — As  a  general  rule  these  are  two  in 
number — superior  and  inferior.  The  superior  ophthalmic  vein 
is  the  larger  of  the  two,  and  it  accompanies  the  artery  across 
the  optic  nerve.  It  takes  origin  at  the  root  of  the  nose, 
where  it  communicates  by  a  wide  radicle  with  the  angular 
vein.  The  inferior  ophthalmic  vein  lies  deeper,  below  the 
level  of  the  optic  nerve,  and  it  is  brought  into  communica- 
tion with  the  pterygoid  venous  plexus  by  an  offset  which 
passes  through  the  spheno  -  maxillary  fissure.  The  two 
ophthalmic  veins  receive  numerous  tributaries  during  their 
n—22  6 


342 


HEAD  AND  NECK 


course  through  the  orbit,  and  finally  they  pass  between  the 
two  heads  of  the  external  rectus  muscle,  and  through  the 
sphenoidal  fissure  to  open  into  the  cavernous  sinus,  either 
separately  or  by  a  common  trunk. 

Recti  Muscles. — The  four  straight  muscles  of  the  eyeball 
converge  to  the  apex  of  the  orbit,  and  together  form  the 
sides  of  a  four-sided  or  pyramidal  space,  in  which  are  en- 
closed the  optic  nerve  and  the  greater  part  of  the  globe  of 
the  eye.  The  rectus  superior,  which  has  been  reflected,  has 
already  been  studied.     The  rectus  internus  springs  from  the 


Frontal  nerve 


Lachrymal  nerve 


Fourth  nerve 


Nasal  nerve 


External  rectus 


Superior  rectus 

Levator  palpebrae 
superioris 

Superior  division  of 
third  nerve 

Fourth  nerve 


Superior  oblique 


Optic  foramen 


Internal  rectus 


Inferior  rectus 

Inferior  division  of 
third  nerve 


Sixth  nerve 
Spheno-maxillary  fissure 

Fig.  126. — Diagram  of  the  Orbital  Cavity,  and  of  the  origin  of  the  ocular 
muscles  in  relation  to  the  optic  foramen  and  the  sphenoidal  fissure,  and 
the  nerves  that  traverse  the  latter. 

inner  side  of  the  optic  foramen,  and  the  rectus  inferior  takes 
origin  from  a  fibrous  band  which  bounds  the  inner  ex- 
tremity of  the  sphenoidal  fissure.  The  rectus  externus  is 
distinguished  from  the  others  by  arising  from  a  fibrous  arch, 
the  extremities  of  which  are  termed  its  two  heads  of  origin. 
The  lower  head  arises  in  common  with  the  rectus  inferior 
from  the  body  of  the  sphenoid,  where  this  bounds  the  inner 
end  of  the  sphenoidal  fissure ;  the  upper  head  is  attached 
above  the  sphenoidal  fissure  upon  the  outer  side  of  the  optic 
foramen,  where  its  origin  becomes  continuous  with  that  of 
the  superior  rectus.  Through  the  archway  which  intervenes 
between  the  two  heads  of  the  external  rectus  pass  the  two 


DISSECTION  OF  THE  ORBIT  343 

divisions    of    the    oculo-motor   nerve,    the    nasal    nerve,   the 
abducent  nerve,  and  the  ophthalmic  veins  (Fig.  126). 

A  better  view  of  these  attachments  may  be  obtained  by  dividing  the 
optic  nerve  close  to  the  optic  foramen  and  turning  forwards  the  eyeball. 

The  manner  in  which  the  recti  muscles  are  inserted  into 
the  eyeball  should  next  be  studied.  Each  ends  in  a  delicate 
membranous  tendon,  which  is  inserted  into  the  sclerotic  coat, 
about  a  quarter  of  an  inch  behind  the  sclero-corneal  junction. 

Third  Nerve  (nervus  oculomotorius). — The  two  divisions 
of  this  nerve  enter  the  orbit  through  the  sphenoidal  fissure, 
between  the  two  heads  of  the  external  rectus.  The  superior 
division  has  been  traced  to  the  rectus  superior  and  the  levator 
palpebrae  superioris.  The  inferior  division  is  much  the  larger 
of  the  two,  and  almost  immediately  divides  into  three  branches 
for  the  supply  of  the  rectus  internus,  the  rectus  inferior,  and 
the  obliquus  inferior.  The  nerves  to  the  two  recti  enter  the 
ocular  surfaces  of  these  muscles ;  the  nerve  to  the  inferior 
oblique  is  a  long  branch,  which  is  prolonged  forwards  in  the 
interval  between  the  rectus  inferior  and  rectus  externus,  and 
enters  the  hinder  border  of  the  inferior  oblique  muscle.  Soon 
after  its  origin  this  branch  gives  the  short  motor  root  to  the 
lenticular  ganglion,  and  likewise  supplies  two  or  three  ad- 
ditional filaments  to  the  inferior  rectus  muscle. 

Sixth  Nerve  (nervus  abducens). — The  sixth  nerve  will  be 
found  closely  applied  to  the  ocular  surface  of  the  external 
rectus,  and  it  enters  the  orbit  by  passing  through  the  narrow 
interval  between  the  heads  of  this  muscle.  It  is  destined 
entirely  for  the  supply  of  the  rectus  externus. 

Arrangement  of  the  Nerves  in  the  Sphenoidal  Fissure. — 
Now  that  the  orbit  is  dissected,  and  the  various  nerves  which 
were  met  in  the  dissection  of  the  cavernous  sinus  traced  into 
the  cavity,  the  dissector  will  observe  that  the  arrangement  of 
these  nerves  in  the  sphenoidal  fissure  is  somewhat  different 
from  that  in  the  sinus. 

The  lachrymal,  frontal,  and  trochlear  or  fourth  nerves 
enter  the  orbit  above  the  muscles  on  very  much  the  same 
plane  (Fig.  126).  The  other  nerves  enter  between  the  heads 
of  the  external  rectus.  Of  these  the  superior  division  of  the 
oculo-motor  nerve  is  the  highest,  next  comes  the  nasal  nerve, 
then  the  inferior  division  of  the  oculo-motor  nerve,  whilst  the 
abducent  nerve  occupies  the  lowest  level. 
11— 22  c 


344 


HEAD  AND  NECK 


J)issection. — The  inferior  oblique  muscle  is  placed  very  differently  from 
the  other  muscles  of  the  orbit.  It  is  situated  below  the  eyeball,  and  turns 
round  its  inferior  and  outer  surface.  It  must  be  dissected  from  the  front. 
It  is  necessary,  therefore,  to  restore  the  eyeball  to  its  natural  place.  Next, 
evert  the  lower  eyelid  and  remove  the  conjunctiva  from  its  deep  surface  as 
it  is  reflected  on  to  the  globe  of  the  eye.  A  little  dissection  in  the  floor  of 
the  fore-part  of  the  orbit  and  the  removal  of  some  fat  will  reveal  the  inferior 
oblique  muscle. 


Levator  palpebrte  super 
Superior  rect 

Superior  oblique 
Lachrymal  gland  — 

External  rectus 

Sixth  nerve 

Lenticular  ganglion 
Nasal  nerve 


Ophthalmic  division 

of  fifth  nerve 

Superior  maxillary 

division  of  fifth  nerve 

Motor  root  of 
fifth  nerve 


trochlea 


I    l'|HJ\l  3*7 — Superior  oblique 


Inferior  rectus 
Internal  rectus 


—  Fourth  nerve 
i==-  Sixth  nerve 


Optic  nerve 


Gasserian  ganglion 

Inferior  maxillary  division 
of  fifth  nerve 


Third  nerve 


Sixth  nerve 
Fourth  nerve 


Fig.  127. — Dissection  of  the  Orbit  and  the  Middle  Cranial  Fossa.      Both 
roots  of  the  fifth  nerve  with  Gasserian  ganglion  are  turned  outwards. 

Inferior  Oblique  (musculus  obliquus  inferior). — This  muscle 
arises  from  a  small  depression  on  the  orbital  plate  of  the 
superior  maxillary  bone  immediately  to  the  outer  side  of  the 
opening  of  the  nasal  duct.  It  passes  outwards  below  the 
inferior  rectus  muscle,  and,  inclining  slightly  backwards,  ends 
in  a  thin  membranous  tendon,  which  gains  insertion  into  the 
outer  aspect  of  the  sclerotic  coat  of  the  eyeball  under  cover 
of  the  rectus  externus.  This  insertion  is  not  far  from  that  of 
the  superior  oblique,  but  is  placed  farther  back.      A  branch 


DISSECTION  OF  THE  ORBIT  345 

of  the  inferior  division  of  the  third  nerve  has  been  traced  to 
the  posterior  margin  of  the  inferior  oblique  muscle. 

Capsule  of  Tenon  (fascia  bulbi). — This  is  a  firm,  loose 
membrane  in  relation  to  the  globe  of  the  eye.  Its  con- 
nexions are  somewhat  complicated,  and  they  cannot  in  every 
detail  be  satisfactorily  displayed  in  an  ordinary  dissection. 
It  may  be  studied  from  a  threefold  point  of  view — (1)  in  its 
connexion  with  the  eyeball;  (2)  in  its  connexions  with  the 
muscles  inserted  into  the  globe  of  the  eye ;  and  (3)  in  its 
connexions  with  the  walls  of  the  orbit. 

The  relation  which  the  capsule  of  Tenon  exhibits  to  the 
eyeball  is  very  simple.  The  membrane  is  spread  over  the 
posterior  five-sixths  of  the  globe — the  cornea  alone  being  free 
from  it.  In  front,  it  lies  under  the  ocular  conjunctiva,  with 
which  it  is  intimately  connected,  and  it  ends  by  blending 
with  the  conjunctiva  close  to  the  margin  of  the  cornea. 
Behind,  it  fuses  with  the  sheath  of  the  optic  nerve,  where  the 
latter  pierces  the  sclerotic.  The  anterior  surface  of  the 
membrane  (i.e.,  the  surface  towards  the  globe  of  the  eye)  is 
smooth,  and  is  connected  to  the  eyeball  by  some  soft  yielding 
and  humid  areolar  tissue,  the  interval  between  them  in  fact 
constituting  an  extensive  lymph  space.  Its  posterior  surface 
is  in  contact  with  the  orbital  fat,  to  which  it  is  loosely  ad- 
herent, while  farther  forwards,  as  we  have  noted,  this  surface 
is  firmly  attached  to  the  ocular  conjunctiva.  It  is  apparent, 
therefore,  that  by  this  membrane  a  socket  is  formed  for  the 
eyeball,  in  which  it  can  glide  with  the  greatest  freedom. 

The  tendons  of  the  various  ocular  muscles  are  inserted 
into  the  eyeball  within  this  capsule,  and  they  gain  its  interior 
by  piercing  the  membrane  opposite  the  equator  of  the  globe 
(Fig.  128).  The  lips  of  the  openings  through  which  the  four 
recti  muscles  pass  are  prolonged  backwards  upon  the  muscles, 
in  the  form  of  sheaths,  very  much  in  the  same  manner  that 
the  infundibuliform  fascia  is  prolonged  upon  the  spermatic 
cord  from  the  internal  abdominal  ring.  These  sheaths 
gradually  become  more  and  mpre  attenuated  until  at  last 
they  blend  with  the  perimysium  of  the  muscular  bellies.  In 
the  case  of  the  superior  oblique  muscle  the  corresponding 
prolongation  is  only  related  to  its  reflected  portion  ;  it  reaches 
the  pulley,  and  there  it  ends  by  becoming  attached  to  its 
margin.  The  sheath  of  the  inferior  oblique  may  be  traced 
upon  the  muscle  as  far  as  the   floor  of  the  orbit.      The  inner 


,46 


HEAD   AND   NECK 


or  ocular  edge  of  each  of  the  four  apertures  through  which 
the  recti  muscles  pass  is  strengthened  by  a  slip  of  fibrous 
tissue  (Lockwood).  The  importance  of  these  slips  will  be 
understood  when  we  remember  that  the  capsule  of  Tenon  is 
at  various  points  firmly  bound  to  the  bony  wall  of  the  orbit. 
They  therefore  act  as  pulleys,  and  protect  the  globe  of  the 
eye  from  pressure  during  contraction  of  the  muscles.  The 
aperture  for  the  superior  oblique  is  not  furnished  with  such  a 
slip,  and  it  is  doubtful  if  the  opening  for  the  inferior  oblique 
muscle  possesses  one. 

Dissection. — An  admirable  view  of  the  relations  which  the  capsule  of 
Tenon  presents  to  the  eyeball  and  the  tendons  of  the  ocular  muscles  can 


___-     Tendon  of  superior  oblique 
Tendon  of  superior  rectus 

Tendon  of  external  rectus 

Cut  edge  of  capsule  of 
Tenon  and  conjunctiva 

Tendon  of  inferior  rectus 


Tendon  of  internal  rectus 

Fig.  128. — Dissection  of  the  Capsule  of  Tenon  from  the  front. 


Capsule  of  Tenon  thrown 
back  from  eyeball 


be  obtained  by  the  following  dissection  : — Divide  the  outer  canthus  of  the 
eyelids  as  far  out  as  the  margin  of  the  orbital  opening.  Pull  the  eyelids 
widely  apart,  so  as  to  expose  as  much  as  possible  of  the  anterior  face  of 
the  eyeball.  Next  divide  the  conjunctiva  by  a  circular  incision  just  outside 
the  cornea.  At  this  point  the  capsule  of  Tenon  is  so  intimately  connected 
with  the  conjunctiva  that  it  is  divided  at  the  same  time.  Now  raise  care- 
fully both  conjunctiva  and  Tenon's  capsule  from  the  surface  of  the  eyeball, 
and  spread  them  out  round  the  orbital  opening,  as  is  depicted  in  Fig.  128. 
The  openings  in  the  capsule  of  Tenon  for  the  tendons  of  the  ocular  muscles 
and  the  thickened  margins  of  these  apertures  are  well  seen.  Note  also  the 
sheaths  which  are  given  to  the  muscles. 

Check  and  Suspensory  Ligaments. — The  connexions  of 
the  capsule  of  Tenon  to  the  walls  of  the  orbital  cavity  are 
somewhat  complicated.  The  suspe?isory  ligament  (Lockwood) 
plays  an  important  part  in  this  respect.      It  stretches  across 


DISSECTION  OF  THE  ORBIT  347 

the  fore-part  of  the  orbit,  after  the  fashion  of  a  hammock, 
and  gives  support  to  the  eyeball.  Its  two  extremities  are 
narrow,  and  are  attached  respectively  to  the  malar  and 
lachrymal  bones.  Below  the  eyeball  it  widens  out  and  forms 
a  part  of  the  capsule  of  Tenon.  The  external  and  internal 
check  ligaments  also  constitute  bonds  of  union  between  the 
capsule  of  Tenon  and  the  orbital  wall.  They  are  strong 
bands  which  pass  from  the  sheaths  around  the  external  and 
internal  recti  muscles  to  obtain  attachment  to  the  malar  and 
lachrymal  bones  respectively ;  here  they  are  brought  into 
association  with  the  extremities  of  the  suspensory  ligament. 
The  function  of  the  check  ligaments  is  easily  understood. 
They  limit  the  contraction  of  the  external  and  internal  recti 
muscles,  and  thus  prevent  excessive  rotation  of  the  eyeball  in 
an  outward  or  inward  direction.  There  is  a  similar  but  less 
direct  provision  by  means  of  which  the  action  of  the  superior 
and  inferior  recti  muscles  is  limited.  The  action  of  the 
former  muscle  is  checked  through  its  intimate  connexion 
with  the  levator  palpebral  superioris  in  the  fore-part  of  the 
orbit ;  the  action  of  the  inferior  rectus  is  checked  through  its 
connexion  with  the  suspensory  ligament. 

Dissection. — In  order  that  the  temporo-malar,  or  orbital  branch  of  the 
superior  maxillary  division  of  the  trigeminal  nerve,  may  be  displayed  in  its 
course  through  the  orbit,  the  orbital  contents  must  be  removed.  It  will 
then  be  found  in  the  midst  of  a  little  soft  fat  in  the  angle  between  the  floor 
and  outer  wall  of  the  orbit. 

Temporo-malar  Nerve  (nervus  zygomaticus). — This  small 
nerve  arises  in  the  spheno-maxillary  fossa,  from  the  superior 
maxillary  division  of  the  trigeminal  nerve,  and  it  enters  the 
orbit  by  passing  through  the  spheno-maxillary  fissure.  It 
almost  immediately  divides  into  two  terminal  branches — viz., 
the  temporal  and  the  malar. 

The  temporal  branch  (ramus  zygomaticotemporal)  runs 
forwards  and  upwards  upon  the  outer  wall  of  the  orbit,  under 
cover  of  the  periosteum,  and,  after  receiving  a  communicating 
twig  from  the  lachrymal  nerve,  it  enters  the  temporal  canal 
of  the  malar  bone.  This  conducts  it  to  the  fore-part  of  the 
temporal  region,  where  it  has  already  been  examined  (pp.  109 
and  265). 

The  ?nalar  branch  (ramus  zygomaticofacialis)  continues 
forward  in  the  angle  between  the  floor  and  outer  wall  of  the 
orbit,  and  is  finally  conducted  to  the  face  by  a  minute  canal 


348  HEAD  AND  NECK 

which  perforates  the  malar  bone.      Here  it  has  been  displayed 
in  the  dissection  of  the  face  (p.  265). 


PREVERTEBRAL  REGION. 

The  following  are  the  structures  to  be  displayed  in   this 
dissection  : — 


Prevertebral  muscles. 
Intertransverse  muscles. 
Cervical  nerves. 
Vertebral  artery. 


Vertebral  vein. 

Vertebral  and  cranio-vertebral 
articulations. 


Dissection. — In  order  that  we  may  obtain  a  proper  view  of  the  pharynx 
and  the  prevertebral  muscles,  it  is  necessary  to  make  a  somewhat  complicated 
dissection.  The  fore-part  of  the  skull  bearing  the  pharynx  must  be  separated 
from  the  back  part  of  the  skull  and  the  cervical  portion  of  the  vertebral 
column.  Place  the  preparation  upside  down,  so  that  the  cut  margin  of  the 
skull  rests  upon  the  table,  and,  having  divided  the  common  carotid  artery, 
the  internal  jugular  vein,  the  vagus  nerve,  and  the  sympathetic  cord  on 
each  side  at  the  level  of  the  neck  of  the  first  rib,  draw  the  trachea  and 
cesophagus,  together  with  the  great  blood  vessels  and  nerves,  forwards 
from  the  anterior  surface  of  the  vertebral  column.  This  separation  must 
be  effected  right  up  to  the  base  of  the  skull.  At  this  point  great  caution 
must  be  observed,  otherwise  the  pharyngeal  wall  or  the  insertions  of  the 
prevertebral  muscles  will  be  damaged.  The  base  of  the  skull  having  been 
reached,  the  point  of  the  knife  should  be  carried  across  the  basilar  process 
of  the  occipital  bone  between  the  pharynx  and  the  vertebral  muscles,  so  as 
to  divide  the  thick  investing  periosteum. 

The  basilar  process  must  now  be  divided  by  means  of  a  chisel.  Still 
retaining  the  part  upside  down,  place  the  skull  so  that  its  floor  rests  upon 
the  end  of  a  wooden  block.  Then  apply  the  edge  of  the  chisel  to  the  under 
surface  of  the  basilar  process,  adjust  it  accurately  in  the  interval  between 
the  pharyngeal  wall  and  the  prevertebral  muscles,  and  with  a  wooden 
mallet  drive  it  through  the  base  of  the  skull,  inclining  it,  at  the  same  time, 
slightly  backwards. 

The  next  step  in  the  dissection  consists  in  making  two  saw-cuts  through 
the  cranial  wall.  The  head  having  been  placed  upon  its  side,  the  saw 
must  be  applied  to  the  outer  aspect  of  the  skull  half  an  inch  behind  the 
mastoid  process,  and  carried  obliquely  forwards  and  inwards  to  reach  a 
point  immediately  behind  the  jugular  foramen.  The  same  saw-cut  must 
be  repeated  upon  the  opposite  side  of  the  head. 

To  complete  the  dissection  the  dissector  must  again  have  recourse  to  the 
chisel.  Placing  the  preparation  so  that  the  floor  of  the  cranium  looks 
upwards,  divide  the  base  of  the  skull,  on  each  side,  in  the  interval  between 
the  petrous  portion  of  the  temporal  bone  and  the  basilar  portion  of  the 
occipital  bone.  In  front,  this  cut  should  reach  the  outer  extremity  of  the 
incision  already  made  through  the  basilar  process  ;  whilst  behind,  it  should 
be  carried  backwards  upon  the  inner  side  of  the  jugular  foramen  to  reach 
the  inner  end  of  the  saw-cut.  When  this  has  been  done  upon  both  sides 
of  the  basilar  process,  the  fore-part  of  the  skull  carrying  the  pharynx  and 
the  great  blood-vessels  and  nerves  can  be  separated  from  the  back  part  of 
the  skull  and  cervical  portion  of  the  vertebral  column.     The  only  large 


PREVERTEBRAL  REGION  349 

nerve  which  will  be  divided  is  the  hypoglossal,  but,  as  it  is  cut  close  to  the 
basis  cranii,  and  below  this  it  is  firmly  connected  with  the  trunk  ganglion 
of  the  vagus,  it  retains  its  position. 

The  pharynx  and  anterior  portion  of  the  skull  should  now  be  covered 
with  a  piece  of  cloth  soaked  in  the  spirit  and  carbolic  solution,  and  the 
whole  enveloped  in  an  oil-cloth  wrapper.  It  can  then  be  laid  aside  until 
the  dissection  of  the  prevertebral  region  and  the  ligaments  of  the  cervical 
vertebrae  and  the  occiput  have  been  studied. 

Returning  to  the  posterior  part  of  the  skull  and  the  cervical  portion  of 
the  spine,  the  dissector  should  proceed  to  define  the  attachments  of  the 
muscles  which  lie  in  front  of  the  transverse  processes  and  the  bodies  of  the 
vertebrae.     These  are  three  in  number  on  each  side,  viz.  : — 

1.   The  longus  colli.  2.   The  rectus  capitis  anticus  major. 

3.   The  rectus  capitis  anticus  minor. 

Longus  Colli. — This  is  the  most  powerful  of  the  prevertebral 
muscles,  and  it  lies  nearest  to  the  mesial  plane.  Its  con- 
nexions are  somewhat  intricate,  but  when  it  has  been 
thoroughly  cleaned  it  will  be  seen  to  consist  of  three  portions 
— viz.,  an  upper  and  lower  oblique  part,  and  an  intermediate 
vertical  part. 

The  lower  oblique  division  of  the  longus  colli  arises  from 
the  lateral  aspect  of  the  bodies  of  the  upper  two  or  three 
dorsal  vertebrae.  It  extends  upwards  and  slightly  outwards, 
and  ends  in  two  tendinous  slips  which  are  inserted  into 
the  anterior  tubercles  of  the  transverse  processes  of  the 
fifth  and  sixth  cervical  vertebrae.  In  the  interval  between 
this  portion  of  the  longus  colli  and  the  scalenus  anticus,  the 
vertebral  artery  will  be  observed.  The  upper  oblique  part  of 
the  longus  colli  arises  by  three  tendinous  slips  from  the 
anterior  tubercles  of  the  transverse  processes  of  the  third, 
fourth,  and  fifth  cervical  vertebrae,  and  tapers  somewhat 
as  it  proceeds  upwards  and  inwards,  to  obtain  a  pointed 
and  tendinous  insertion  into  the  anterior  tubercle  of  the 
atlas.  The  vertical  part  of  the  muscle  is  much  the  largest 
of  the  three  divisions,  and  it  lies  along  the  inner  side 
of  the  oblique  portions,  with  both  of  which  it  is  more  or 
less  intimately  connected.  Thus,  below,  it  arises  in  common 
with  the  inferior  oblique  part  by  two  or  three  slips  from 
the  sides  of  the  bodies  of  the  upper  two  or  three  dorsal 
vertebrae ;  above  this  it  derives  additional  slips  of  origin  from 
the  bodies  of  the  lower  two  cervical  vertebrae  ;  lastly,  its  outer 
border  is  reinforced  by  slips  from  the  transverse  processes 
of  the  lower  three  or  four  cervical  vertebrae.  It  stretches 
vertically  upwards  and  is  inserted  upon  the  inner  side  of  the 


35° 


HEAD  AND  NECK 


upper  oblique  part  of  the  muscle,  by  three  tendinous  processes, 
which  obtain  attachment  to  the  bodies  of  the  second,  third, 
and  fourth  cervical  vertebrae. 

Rectus  Capitis  Anticus  Major. — The  rectus  capitis  anticus 


Rectus  lateralis 

Rectus  capitis 
anticus  minor 

Rectus  capitis 
anticus  major 


L0112US  i.ulli 


Fig.  i 29. —Prevertebral  Muscles  of  the  Neck.      On  the  right  side  the  rectus 
capitis  anticus  major  has  been  removed.     (Paterson. ) 

major  is  an  elongated  muscle  which  arises  by  four  tendinous 
slips  from  the  anterior  tubercles  of  the  transverse  processes 
of  the  third,  fourth,  fifth,  and  sixth  cervical  vertebrae,  and 
is  inserted  in  front  of  the  foramen  magnum,  upon  the  under 
aspect  of  the  basilar  process  of  the  occipital  bone.  To 
reach   this  insertion   the  muscle  inclines  slightly  inwards  as 


PREVERTEBRAL  REGION  351 

it  ascends  upon   the  front  of  the  vertebral  column.       It  is 
supplied  by  twigs  from  the  first  loop  of  the  cervical  plexus. 

Rectus  Capitis  Anticus  Minor. — This  is  a  small  muscle. 
It  is  in  great  part  concealed  by  the  upper  part  of  the 
preceding  muscle,  which  should  be  detached  from  its 
insertion,  and  turned  downwards  so  as  to  bring  it  fully 
into  view.  It  arises  from  the  anterior  aspect  of  the  root  of 
the  transverse  process  of  the  atlas,  and  proceeding  upwards 
and  inwards  is  inserted  into  the  under  surface  of  the  basilar 
process  of  the  occipital  bone  behind  the  rectus  capitis  anticus 
major.  It  is  supplied  by  a  filament  from  the  first  loop  of 
the  cervical  plexus. 

Before   proceeding   farther,    the    dissector    should    again    examine    the 
attachments  of  the  scalene  muscles  [v.  p.  216). 

Intertransverse  Muscles  (musculi  intertransversarii). — To 
obtain  a  proper  display  of  the  intertransverse  muscles  it  will 
be  necessary  to  remove  the  prevertebral  and  scalene  muscles. 
The  intertransverse  muscles  consist  of  seven  pairs  of  small 
fleshy  slips,  on  each  side,  which  connect  the  bifid  extremities 
of  the  cervical  transverse  processes.  The  anterior  slip  of 
each  muscle  is  attached  to  the  anterior  tubercles  of  two 
adjacent  transverse  processes  ;  whilst  the  posterior  slip  extends 
between  the  posterior  tubercles.  The  highest  pair  of  muscular 
slips  lies  between  the  atlas  and  the  axis ;  the  lowest  pair 
connects  the  transverse  process  of  the  seventh  cervical  vertebra 
with  the  transverse  process  of  the  first  dorsal  vertebra. 

Cervical  Nerves. — The  cervical  spinal  nerves  will  be 
observed  to  have  a  very  definite  relation  to  the  intertransverse 
muscles.  The  anterior  primary  branches  of  the  lower  six 
cervical  nerves  make  their  appearance  by  passing  outwards 
between  the  two  slips  of  the  corresponding  muscles.  The 
posterior  primary  divisions  of  the  same  nerves  turn  backwards 
behind  the  posterior  muscular  slips. 

The  upper  two  cervical  nerves  emerge  from  the  spinal 
canal  differently  from  the  others.  They  pass  backwards 
over  the  neural  arches  of  the  atlas  and  axis  respectively. 
The  first  or  suboccipital  nerve  has  been  sufficiently  examined 
at  a  previous  stage  of  the  dissection  (p.  322);  but  the 
dissector  is  now  in  a  position  to  observe  that  the  anterior 
primary  division  of  ""the  second  cervical  nerve  turns  forwards 
under  cover  of  the  posterior  slip    of  the   first  intertransverse 


352 


HEAD  AND  NECK 


muscle,  and  winds  round  the  outer  side  of  the  vertebral  artery, 
to  appear  in  front  of  the  anterior  slip  of  the  same  muscle. 

Dissection. — The  vertebral  artery  as  it  traverses  the  succession  of 
foramina  in  the  transverse  processes  of  the  cervical  vertebrae  should  now 
be  exposed.  Remove  the  intertransverse  muscles  as  well  as  the  muscles 
still  attached  to  the  transverse  process  of  the  atlas — viz.,  the  rectus  lateralis, 
the  inferior  oblique,  and  the  superior  oblique.  The  anterior  tubercles  and 
the  costal  portions  of  the  transverse  processes  of  the  third,  fourth,  fifth, 
and  sixth  cervical  vertebra?  should  then  be  snipped  off  by  the  bone  pliers. 


Posterior  arch  of  atlas 


Posterior  primary  divisions 
of  spinal  nerves 


Fig.   130. — Dissection  of  the  Ligamentum  Nuchae  and  of  the  Vertebral 
Artery  in  the  Neck. 

Vertebral  Artery  (arteria  vertebralis).  —  This  vessel  has 
previously  been  traced  to  the  point  where  it  disappears 
through  the  foramen  in  the  transverse  process  of  the  sixth 
cervical  vertebra  ;  it  is  now  seen  to  proceed  vertically  upwards 
through  the  succession  of  foramina  transversaria  until  it 
reaches  the  foramen  in  the  transverse  process  of  the  axis. 
In  this  it  is  directed  outwards  in  order  that  it  may  gain  the 
more  outwardly  placed  foramen  of  the  atlas.  Upon  the 
upper  surface  of  the  atlas  it  again  changes  its  direction  and 
proceeds  backwards,  behind  the  lateral  mass,  in  a  groove  on 
the  upper  surface  of  the  posterior  arch  of  that  bone.      Finally, 


PREVERTEBRAL  REGION  353 

it  turns  forwards  under  the  posterior  occipito-atlantal  liga- 
ment, pierces  the  dura  mater,  and  enters  the  cranium  through 
the  foramen  magnum. 

The  vertebral  artery  is  accompanied  by  a  sympathetic 
plexus  of  nerves  derived  from  the  inferior  cervical  ganglion, 
whilst  the  vertebral  vein  breaks  up  in  a  plexiform  manner 
around  it.  The  anterior  divisions  of  the  lower  six  cervical 
nerves  pass  outwards  behind  it ;  the  corresponding  division 
of  the  first  cervical  nerve  passes  forwards  internal  to  it,  whilst 
that  of  the  second  nerve  turns  forward  upon  its  outer  aspect ; 
lastly,  the  posterior  primary  division  of  the  first  cervical  nerve 
enters  the  suboccipital  triangle  of  the  neck  by  passing  back- 
wards between  the  artery  and  the  neural  arch  of  the  atlas. 

The  branches  which  are  given  off  by  the  vertebral  artery 
in  the  neck  are  of  small  size.  They  are  (a)  muscular ;  (b) 
lateral  spinal. 

The  muscular  twigs  go  to  the  muscles  in  the  neighbourhood. 
The  lateral  spinal  branches  enter  the  spinal  canal  upon  the 
cervical  nerves,  and  have  been  described  on  p.  158. 

Vertebral  Vein. — The  vertebral  vein  does  not  take  origin 
within  the  cranium.  It  merely  accompanies  the  vertebral 
artery  in  the  cervical  part  of  its  course,  and  forms  a  close 
venous  plexus  around  it  as  it  proceeds  through  the  succession 
of  bony  foramina  in  the  transverse  processes  of  the  cervical 
vertebrae.  Its  radicles  arise  in  the  suboccipital  region,  where 
they  anastomose  with  the  tributaries  of  the  occipital  and 
deep  cervical  veins.  Before  it  enters  the  transverse  process 
of  the  atlas  it  receives  a  large  offset  from  the  intra-spinal 
venous  plexus.  Inferiorly,  the  vertebral  vein  opens  into  the 
innominate  vein  (p.  221). 

Dissection. — The  muscles  must  now  be  completely  removed,  in  order 
that  the  vertebral  and  cranio-vertebral  joints,  and  the  ligaments  in  con- 
nexion with  the  cervical  portion  of  the  spine,  may  be  examined. 


The  Joints  of  the  Neck. 

The  axis,  atlas,  and  occipital  bone  present  a  scries  of 
articulations  in  which  the  uniting  apparatus  is  very  different 
from  that  of  the  vertebrae  below. 

Articulations  of  the  Lower  Five  Cervical  Vertebrae. — The 
lower  five  cervical  vertebrae  are  united  together  very  much 

vol.  11-    23 


;54 


HEAD  AND  NECK 


upon  the  same  plan  as  the  vertebrae  in  other  regions  of  the 
vertebral  column.  Both  the  bodies  and  the  neural  arches 
are  connected  by  distinct  articulations  and  special  ligaments. 

Three  separate  joints  may  be  said  to  exist  between  the 
opposed  surfaces  of  the  bodies  of  two  adjacent  vertebrae — 
viz.,  a  central  amphiarthrodial  joint  and  two  small  lateral 
diarthrodial  joints. 

The  amphiarthrodial  joint  occupies  by  far  the  greatest 
part  of  the  space  which  exists  between  the  vertebral  bodies, 
and  it  presents  the  usual  characters  of  such  an  articulation. 
The  opposed  bony  surfaces  are  coated  by  a  thin  layer 
of  hyaline  or  encrusting  cartilage,  and  are  brought  into 
direct  union   by  an  interposed  disc  of  fibro-cartilage.     The 


'^W ""'."■"''*'  '  His ';Ki 


Joint  between 
articular  processes 


Synovial  part  of 
joint  between  bodies 
of  vertebrae 


Capsule  around 
joint  between  two 
articular  processes 


Intervertebral  disc 


FlG.  131. — Coronal  section  through  bodies  of  certain  of  the 
Cervical  Vertebrae. 


intervertebral  discs  are  distinctly  deeper  in  front  than  behind, 
and  upon  this  the  cervical  curvature  of  the  column  in  great 
measure  depends. 

The  two  diarthrodial  joints  are  placed  one  on  each  side, 
where  the  disc  of  fibro-cartilage  fails.  They  are  of  small 
extent,  and  are  confined  entirely  to  the  intervals  between  the 
projecting  lateral  lips  of  the  upper  surface  of  the  centrum, 
and  the  bevelled-off  lateral  margins  of  the  lower  surface  of 
the  vertebral  body  immediately  above.  Here  the  bony 
surfaces  are  coated  with  encrusting  cartilage,  and  are  separated 
by  a  synovial  cavity  protected  on  the  outer  side  by  a  feeble 
capsular  ligament. 

The  ligaments  which  bind  the  bodies  of  the  five  lower 
cervical  vertebrae  together  are  the  direct  continuation  upwards 
of  the  anterior  and  the  posterior  common  ligaments  of  the 


JOINTS  OF  THE  NECK  355 

spine.  In  the  removal  of  the  spinal  cord,  the  laminae  of  the 
vertebrae  below  the  axis  have  been  taken  away  so  that  very 
little  dissection  will  be  required  to  make  out  the  connexions 
of  both  of  these  ligaments.  The  anterior  co??imon  ligament  is 
a  strong  band  placed  in  front  of  the  vertebral  bodies.  It  is 
more  firmly  fixed  to  the  intervening  intervertebral  discs  than 
to  the  bones.  The  posterior  common  ligament  which  lies  on 
the  posterior  aspect  of  the  vertebral  bodies  constitutes  the 
anterior  boundary  of  the  spinal  canal.  In  the  cervical  region 
it  completely  covers  the  bodies  of  the  vertebrae,  and  does  not 
present  the  denticulated  appearance  which  is  so  characteristic 
of  it  lower  down.  It  is  chiefly  attached  to  the  cartilaginous 
discs  and  the  adjacent  margins  of  the  bones. 

The  neural  arches  of  the  lower  five  cervical  vertebrae  are 
bound  together  by  (a)  the  articulations  between  the  articular 
processes;  (b)  ligamenta  subflava;  (c)  by  interspinous  liga- 
ments ;  and  (d)  intertransverse  ligaments. 

The  joints  between  the  opposing  articular  processes  are  of 
the  diarthrodial  variety.  The  surfaces  of  bone  are  coated 
with  encrusting  cartilage;  there  is  a  joint  cavity  lined  by 
synovial  membrane,  and  surrounded  by  a  distinct  capsular 
ligament.  This  ligament  is  more  laxly  arranged  in  the  neck 
than  in  the  lower  regions  of  the  spine. 

The  ligamenta  subflava  may  be  examined  on  the  laminae  which  were 
removed  for  the  display  of  the  spinal  cord,  and  which  the  dissector  was 
directed  to  retain.  In  this  specimen  they  may  be  studied  in  the  cervical, 
dorsal,  and  lumbar  regions  of  the  spine.  They  fill  up  the  gaps  between 
the  laminae  of  the  vertebrae,  and  can  be  best  seen  when  the  fore  aspect  of 
the  specimen  is  viewed. 

The  ligamenta  sub/lava  (ligamenta  flava)  are  composed  of 
yellow  elastic  tissue,  and  each  ligament  is  attached  superiorly 
to  the  anterior  surface  and  inferior  margin  of  the  lamina  of 
the  vertebra  above,  whilst  inferiorly  it  is  fixed  to  the  posterior 
surface  and  superior  margin  of  the  lamina  of  the  vertebra 
next  below.  In  this  way  they  form  with  the  laminae  a  smooth, 
even  posterior  wall  for  the  spinal  canal.  Each  ligament 
extends  from  the  posterior  part  of  the  articular  processes  to 
the  mesial  plane,  where  it  is  in  contact  by  a  free  thickened 
inner  border  with  its  neighbour  of  the  opposite  side.  The 
mesial  slit  between  them  in  each  interneural  space  is  filled  by 
some  lax  connective  tissue,  and  it  allows  the  egress  from  the 
spinal  canal  of  some  small  veins.      The  width  of  the  ligaments 


356 


HEAD  AND   NECK 


in  the  different  regions  of  the  spine  depends  upon  the  size  of 
the  spinal  canal.  Thus  they  are  widest  in  the  neck  and  in 
the  lumbar  part  of  the  column.  The  ligamenta  subflava,  by 
virtue  of  their  great  strength  and  elasticity,  are  powerful 
agents  in  maintaining  the  curvatures  of  the  spine ;  they  also 
give  valuable  aid  to  the  muscles  in  restoring  the  spine  to  its 
original  position  after  it  has  been  bent  in  a  forward  direction. 
The  interspi?ious  ligaments  are  most  strongly  developed  in 
the  lumbar  regions,  where  they  fill  up  the  intervals  between 
the  adjacent   margins  of  contiguous   spinous   processes.      In 


Pedicle  of 

divided 


Fig.  132. — The  Ligamenta  Subflava  in  the  Lumbar  Region  of  Spine. 

the  dorsal  region,  and  more  especially  in  the  neck,  they  are 
very  weak. 

The  supraspinous  ligaments  are  thickened  bands  which 
connect  the  summits  of  the  spinous  processes.  In  the  neck 
they  are  replaced  by  the  ligamentum  nuchas  (p.  147). 

The  intertra?isverse  ligaments  are  feebly  marked  in  the 
cervical  region,  and  extend  chiefly  between  the  anterior  bars 
of  the  transverse  processes. 

Articulations  of  the  Axis,  Atlas,  and  Occipital  Bone. — 
The  articulations  which  exist  between  these  three  bones  all 
belong  to  the  diarthrodial  class.  Between  the  atlas  and  axis 
there  are  three  such  joints — viz.,  a  pair  between  the  opposed 
articular  processes,  and  a  third  between  the  anterior  face  of 


JOINTS  OF  THE  NECK  35  7 

the  odontoid  process  and  the  posterior  face  of  the  anterior 
arch  of  the  atlas.  Between  the  atlas  and  occipital  bone  there 
is  a  pair  of  joints — viz.,  between  the  occipital  condyles 
and  the  elliptical  cavities  upon  the  upper  aspect  of  the  lateral 
masses  of  the  atlas. 

The  ligaments  connecting  these  three  bones  together  may 
be  divided  into  three  main  groups  as  follows : — 


Ligaments   connecting    atlas 
with  axis,        .     .     . 


'  Anterior  atlanto-axial. 
Posterior  atlanto-axial. 
Capsular. 
I  Transverse  portion  of  the  cruciform    liga- 
ment. 
Accessory  ligaments   of  the    atlanto-axial 
joints. 

T  .  ..  .    |  Anterior  occipito-atlantal. 

Ligaments    connecting   oca- J  Posterior  occipito-atlantal. 
pital  bone  with  atlas,    .     •  [  Capsular. 

f  Posterior  occipito-axial. 
T  .  .  .       Appendices   superior   and   inferior    of    the 

Ligaments    connecting   occi-J        Fcruciform  H^nt. 
pital  bone  with  axis,     .     .     ^  odontoid  0*  check. 

^  Suspensory. 

The  ligaments  which  are  placed  in  relation  to  the  exterior 
of  the  vertebrae  should  first  be  examined.  These  are  the 
anterior  and  posterior  atlanto-axial,  and  the  anterior  and 
posterior  atlanto-occipital.  The  four  capsular  ligaments  may 
also  be  more  or  less  satisfactorily  studied  at  the  same  time. 

Anterior  Atlanto-axial  Ligament  (Fig.  133). — This  may 
be  regarded  as  being  a  continuation  upwards  of  the  anterior 
common  ligament  of  the  spine.  Below,  it  is  attached  to  the 
fore  aspect  of  the  body  of  the  axis,  whilst  above,  it  is  fixed  to 
the  anterior  arch  of  the  atlas.  It  is  thick  and  strong  in  the 
middle,  but  thins  off  towards  the  sides. 

Posterior  Atlanto-axial  Ligament. — This  ligament  fills  up 
the  interval  between  the  laminae  of  the  axis  vertebra  and  the 
posterior  arch  of  the  atlas,  to  the  contiguous  margins  of  which 
it  is  attached.  It  is  broad  and  membranous,  and  is  the  repre- 
sentative, as  its  attachments  show,  of  the  ligamenta  subflava. 
It  is  pierced  on  each  side  by  the  second  cervical  nerve  as 
this  passes  backwards  over  the  neural  arch  of  the  axis. 

Atlanto-axial  Capsular  Ligaments. — These  are  somewhat 
lax,  and  on  removing  the  outer  part  of  each,  the  joint  cavities 
will  be  opened  into. 

Anterior  Atlanto- Occipital    Ligament   dig.   133). — This 


358 


HEAD  AND  NECK 


ligament  extends  from  the  upper  border  of  the  anterior  arch 
of  the  atlas  to  the  under  surface  of  the  basilar  process  of  the 
occipital  bone  in  front  of  the  foramen  magnum.  On  each 
side  of  the  mesial  plane  it  is  thin  and  membranous,  and 
stretches  outwards  so  as  to  abut  against  the  atlanto-occipital 
capsular  ligament.  In  the  middle  line  there  is  an  exceedingly 
strong  cord-like  band,  which  stands  out  in  strong  relief  from 
the  rest   of  the  ligament,   and  is  carried  downwards  to  the 


Basilar  process  of 
occipital  bone 


Dura  mater 

Vertebral  artery  and 
first  cervical  nerve 


Posterior  occipito- 
axial  ligament 


Anterior  atlanto- 
occipital  ligament 
Two  parts  of  tbe  suspensory 
odontoid  ligament 

Appendix  superior 


Anterior  arch  of  atlas 


-Transverse  ligament 
Anterior  atlanto- 
axial ligament 
Appendix  inferior 

Lenticular  disc  ot  cartilage 
between  the  body  of  the  axis 
and  the  odontoid  process 


Fig.  133. — Mesial  section  through  the  Basilar  Process  of 
Occipital  Bone,  the  Atlas,  and  the  Axis.  (From 
Luschka,  slightly  modified.) 

Between  the  posterior  occipito-axial  ligament  and  the  transverse  ligament    a  small 
synovial  bursa  may  be  seen. 


anterior  tubercle  of  the  atlas.  Part  of  its  fibres  are  attached 
to  this,  but  a  certain  proportion  become  continuous  with  the 
central  thickening  of  the  anterior  atlanto-axial  ligament,  and 
through  this  with  the  anterior  common  ligament  of  the 
spine. 

Posterior  Atlanto-Occipital  Ligament. — This  is  a  thin  and 
weak  membrane  which  occupies  the  gap  between  the  posterior 
arch  of  the  atlas  and  the  posterior  border  of  the  foramen 
magnum,  to  both  of  which  it  is  attached.     It  is  very  firmly 


JOINTS  OF  THE  NECK  359 

connected  with  the  dura  mater,  and  on  each  side  it  reaches 
the  atlanto-occipital  capsular  ligament.  Over  each  of  the 
grooves  on  the  posterior  arch  of  the  atlas  for  the  vertebral 
arteries  it  is  deficient ;  here  its  lower  border  forms  an  arch, 
under  which  the  vessel  and  the  first  cervical  nerve  pass.  It 
is  not  uncommon  to  find  this  fibrous  arch  ossified. 

Atlanto- Occipital  Capsular  Ligaments. — These  connect 
the  occipital  condyles  with  the  lateral  masses  of  the  atlas. 
They  completely  surround  the  joints,  and  are  connected  in 
front  with  the  anterior  atlanto-occipital  ligament,  and  behind 
with  the  posterior  atlanto-occipital  ligament. 

The  occipital  bone,  therefore,  round  the  foramen  magnum 
is  attached  by  special  ligaments  to  each  of  the  four  portions 
of  the  atlas — viz.,  to  the  anterior  arch,  to  the  two  lateral 
masses,  and  to  the  posterior  arch. 

Dissection. — The  remaining  ligaments  are  placed  within  the  spinal 
canal  in  connexion  with  its  anterior  wall.  For  their  proper  display  it 
is  therefore  necessary  to  remove  with  the  bone  pliers  the  laminae  of  the 
axis,  and  the  posterior  arch  of  the  atlas.  The  tabular  part  of  the  occipital 
bone  must  likewise  be  taken  away  by  sawing  it  through,  on  each  side, 
immediately  behind  the  jugular  eminence  and  the  condyle,  and  carrying 
the  saw  into  the  foramen  magnum.  The  upper  part  of  the  tube  of  dura 
mater  which  still  remains  in  the  spinal  canal  must  next  be  carefully 
detached.  A  broad  membranous  band  stretching  upwards  over  the 
posterior  aspect  of  the  body  and  odontoid  process  of  the  axis  is  displayed. 
This  is  the  posterior  occipito-axial  ligament  or  membrana  tectoria. 

Posterior  Occipito-axial  Ligament  or  the  Membrana 
Tectoria. —  This  is  a  broad  ligamentous  sheet  which  is 
attached  below  to  the  posterior  aspect  of  the  body  of 
the  axis  vertebra,  where  it  is  continuous  with  the  posterior 
common  ligament  of  the  spine.  It  extends  upwards,  covering 
completely  the  odontoid  process  and  the  anterior  margin  of 
the  foramen  magnum,  and  is  attached  above  to  the  posterior 
grooved  surface  of  the  basilar  process  of  the  occipital  bone. 

Dissection. — Detach  this  ligament  from  the  axis  and  throw  it  upwards 
upon  the  basilar  process  of  the  occipital  bone.  By  this  proceeding  the 
accessory  ligaments  of  the  atlanto-axial  joints  and  the  cruciform  ligament 
are  brought  into  view,  and  very  little  further  dissection  is  required  to 
define  them. 

Accessory  Atlanto-axial  Ligaments  (Fig.  134). — These 
are  two  strong  bands  which  take  origin  from  the  posterior 
aspect  of  the  body  of  the  axis  vertebra  close  to  the  base  of 
the  odontoid  process.      Each   band  passes  upwards  and  out- 


:6o 


HEAD  AND  NECK 


wards,  and  is  attached  to  the  inner  and  hinder  part  of  the 
lateral  mass  of  the  atlas.  To  a  certain  extent  they  assist  the 
odontoid  check  ligaments  in  limiting  the  rotary  movements 
of  the  atlas  upon  the  axis. 

Cruciform  Ligament  (ligamentum  cruciatum)  (Fig.  134). — 
The  cruciform  ligament  is  composed  of  a  transverse  and  a 
vertical  part.  The  transverse  ligament  (ligamentum  trans- 
versum  atlantis)  is  by  far  the  most  important  constituent 
of  this  apparatus.      It  is  a  strong  band  which  stretches  from 


Membrana  tectoria 
rus  superius 


Occipital 
bone 


Suspensory 
ligament 


Check 
ligament 

Crus 

superius 

Transverse 

ligament 


vT- 
Lateral 
mass  of 
atlas 

Atlanto 
axial  joint 

Body  of  axis 


2g=5=xA.  Accessory  atlanto- 
"  axial  ligament 

Crus  inferius 


Membrana  tectoria 


Fig.  134. — Dissection  from  behind  of  Ligaments  connecting  the 
Occipital  Bone,  the  Atlas,  and  the  Axis  with  each  other. 

the  tubercle  on  the  inner  aspect  of  the  lateral  mass  of 
the  atlas  to  the  corresponding  tubercle  on  the  opposite 
side.  With  the  anterior  arch  of  the  atlas  it  forms  a  ring 
which  encloses  the  odontoid  process — the  pivot  around 
which  the  atlas  bearing  the  head  turns.  It  is  separated  from 
the  posterior  aspect  of  the  odontoid  process  by  a  loose  synovial 
membrane  which  extends  forward  on  each  side  until  it  almost 
reaches  the  synovial  membrane  in  connexion  with  the  mesial 
joint  between  the  odontoid  process  and  the  anterior  arch  of 
the  atlas.  Indeed,  in  some  cases  a  communication  exists 
between  the  two  synovial  cavities. 

The  vertical  part  of  the  cruciform  ligament  consists  of  an 


JOINTS  OF  THE  NECK  361 

upper  and  a  lower  limb,  which  are  termed  the  appendices  or 
crura.  Both  are  attached  to  the  dorsal  surface  of  the  trans- 
verse ligament.  The  cms  superius  is  the  longer  and  flatter 
of  the  two,  and  extends  upwards  on  the  posterior  aspect  of 
the  head  of  the  odontoid  process  to  be  attached  to  the 
posterior  aspect  of  the  basilar  process  immediately  beyond 
the  anterior  margin  of  the  foramen  magnum.  The  cms 
in/erius,  much  shorter,  extends  downwards,  and  is  fixed  to  the 
posterior  aspect  of  the  body  of  the  axis  vertebra. 

Dissection. — Detach  the  appendix  superior  from  the  basilar  process, 
and  throw  it  downwards.  The  suspensory  ligament  is  thus  displayed,  and 
a  better  view  of  the  alar  or  check  ligaments  obtained. 

Suspensory  Ligament  (ligamentum  apicis  dentis). — The 
suspensory  ligament  of  the  odontoid  consists  of  two  parts 
— an  anterior  and  a  posterior.  The  posterior  part  is  a 
rounded  cord -like  ligament  which  is  attached  below  to  the 
summit  of  the  odontoid  process,  and  above  to  the  fore 
margin  of  the  foramen  magnum.  This  ligament,  inasmuch 
as  it  is  developed  around  the  continuation  of  the  chorda 
dorsalis  from  the  odontoid  to  the  basis  cranii,  is  a  structure 
of  considerable  morphological  interest.  The  anterior  part  of 
the  suspensory  ligament  is  a  fiat  and  weak  band  which  is 
attached  above  to  the  anterior  margin  of  the  foramen  magnum 
at  the  same  point  as  the  posterior  portion.  Below,  the  two 
portions  are  separated  by  an  interval  filled  with  cellular  tissue, 
and  the  anterior  part  is  attached  to  the  odontoid  process 
immediately  above  its  articular  facet  for  the  anterior  arch  of 
the  atlas. 

Check  or  Alar  Ligaments  (ligamenta  alaria)  (Fig.  134). — 
These  are  very  powerful  bands  which  spring,  one  from  each 
side  of  the  summit  of  the  odontoid  process,  and  proceed 
outwards  and  slightly  upwards  to  be  attached  to  the  inner 
aspect  of  the  condyloid  eminences  of  the  occipital  bone. 
They  limit  rotation  of  the  head,  and  in  this  they  are  aided 
by  the  accessory  atlanto-axial  ligaments. 

Movements. — Nodding  movements  of  the  head  are  permitted  at  the 
occipitoatlantal  articulations.  Rotatory  movements  <>f  the  head  and  atlas 
around  the  odontoid  process,  which  acts  as  a  pivot,  take  place  at  the 
atlanto-axial  joints.  Excessive  rotation  is  checked  by  the  alar  or  check 
ligani' 


362  HEAD  AND  NECK 


MOUTH  AND  PHARYNX. 

The  dissector  must  now  return  to  the  anterior  part  of  the 
skull  which  had  been  laid  aside  while  the  dissection  of  the 
prevertebral  region  was  being  carried  on.  The  mouth  and 
pharynx  should,  in  the  first  instance,  engage  his  attention. 

Mouth. — The  mouth  is  the  expanded  upper  part  of  the 
alimentary  canal.  It  is  placed  in  the  lower  part  of  the  face, 
below  the  nasal  chambers,  and  its  cavity  is  controlled  by 
muscles  which  are  under  the  influence  of  the  will.  The 
mouth  consists  of  two  subdivisions,  viz.,  a  smaller  anterior 
part,  termed  the  vestibule,  which  is  bounded  in  front  by  the 
lips  and  cheeks,  and  behind  by  the  teeth  and  gums,  and  a 
large  part,  the  771011th  proper,  which  is  placed  within  the  teeth. 
The  mucous  lining  of  the  mouth  should  be  thoroughly  cleansed, 
and  the  two  subdivisions  of  the  cavity  examined  from  the 
front  through  the  oral  fissure. 

The  vestibule  of  the  mouth  which  passes  round  the  teeth 
and  gums  is  a  mere  fissure- like  space  except  when  the  cheeks 
are  inflated  with  air.  It  is  into  this  subdivision  of  the  mouth- 
that  the  parotid  duct  opens  (p.  249).  Above  and  below,  it  is 
bounded  by  the  reflection  of  the  mucous  membrane  from  the 
lips  and  cheeks  on  to  the  alveolar  margins  of  the  maxillary 
and  mandibular  bones.  In  front,  it  opens  upon  the  face  by 
means  of  the  oral  fissure,  whilst  posteriorly,  behind  the  last 
molar  tooth,  it  communicates  on  each  side  by  means  of  a 
variable  aperture  with  the  cavity  of  the  mouth  proper.  When 
all  the  teeth  are  in  place  the  existence  of  this  communication 
is  of  importance  in  cases  of  spasmodic  closure  of  the  jaws, 
because  through  it  fluids  may  be  introduced  into  the  posterior 
part  of  the  buccal  cavity  or  mouth  proper. 

In  paralysis  of  the  facial  muscles  the  lips  and  cheeks  fall  away  from  the 
dental  arcades  and  food  is  apt  to  lodge  in  the  vestibule. 

The  mouth  proper  is  that  part  of  the  buccal  cavity  which  is 
placed  within  the  teeth.  It  is  bounded  in  front  and  laterally 
by  the  gums  and  teeth,  whilst  behind  it  communicates  by 
means  of  the  isthmus  faucium  with  the  pharynx.  The  floor 
is  formed  by  the  tongue  and  the  mucous  membrane  which 
stretches  to  this  from  the  inner  aspect  of  the  mandible ;  the 


MOUTH  363 

roof  is  vaulted,  and  is  composed  of  the  hard  and  the  soft 
palate.  Into  this  part  of  the  buccal  cavity  the  ducts  of  the 
submaxillary  glands  (Wharton's  ducts)  and  the  ducts  of  the 
sublingual  glands  (ducts  of  Rivinus)  open  (pp.  301  and  302). 
When  the  mouth  is  closed  the  dorsum  of  the  tongue  is 
usually  applied  more  or  less  closely  to  the  palate,  and  the 
cavity  is  almost  completely  obliterated. 

The  various  parts  which  bound  the  oral  cavity  may  now 
be  examined  in  turn. 

Lips  (labia  oris). — The  structure  of  the  lips  has  in  a  great 
measure  been  already  examined  in  the  dissection  of  the  face 
(p.  258).  Each  lip  may  be  regarded  as  being  composed  of 
four  layers.  From  before  backwards  these  are — (1)  cuta- 
neous; (2)  muscular;  (3)  glandular;  and  (4)  mucous.  The 
skin  and  ??iucous  ??iembrane  become  continuous  with  each 
other  at  the  free  margin  of  the  lip.  From  the  deep  aspect 
of  each  lip  the  mucous  membrane  is  reflected  on  to  the 
alveolar  margin  of  the  corresponding  jaw,  and  in  the  mesial 
plane  it  is  raised  in  the  form  of  a  free  fold.  These  folds  are 
termed  the  frenida ;  in  the  dissection  of  the  face  they  have 
been  more  or  less  destroyed.  The  muscular  layer  constitutes 
the  chief  bulk  of  the  lips.  It  is  formed  by  the  orbicularis 
oris  and  the  various  muscles  which  converge  upon  the  mouth, 
many  of  the  fibres  of  which  are  attached  to  the  skin.  The 
labial  glands  are  very  numerous,  and  lie  in  the  submucous 
tissue  which  intervenes  between  the  mucous  membrane  and 
the  muscular  fibres.  The  ducts  of  these  glands  pierce  the 
mucous  membrane,  and  open  into  the  vestibule.  In  each 
lip  there  is  an  arterial  arch  formed  by  the  corresponding 
coronary  arteries  (p.  268). 

The  lymphatic  vessels  of  both  lips  join  the  submaxillary 
lymphatic  glands.  This  has  an  important  bearing  in  con- 
nexion with  epithelioma  of  the  lip. 

Cheeks  (buccae). — The  cheeks  have  five  layers  entering 
into  their  construction,  all  of  which  have  been  examined  in 
the  dissection  of  the  face.  They  are — (1)  skin;  (2)  a  fatty 
layer  traversed  by  some  of  the  facial  muscles  and  the  facial 
artery;  (3)  the  buccal  aponeurosis;  (4)  the  buccinator  muscle; 
(5)  the  mucous  membrane.  Numerous  buccal  glands,  similar 
in  character  to  the  labial  glands,  lie  in  the  submucous  tissue 
between  the  mucous  membrane  and  the  buccinator  muscle. 
Four  or  five  mucous  glands  of  larger  size,  termed  the  molar 


364 


HEAD  AND  NECK 


glands,  occupy  a  more  superficial  position.  They  lie  upon 
the  buccal  aponeurosis,  close  to  the  point  where  this  is  pierced 
by  the  parotid  duct,  and  their  ducts  also  open  into  the  vesti- 
bule of  the  mouth.  The  buccal  aponeurosis  is  a  dense  fascia 
which  covers  the  buccinator  muscle.  Above  and  below,  it  is 
attached  to  the  alveolar  portions  of  the  maxillary  and  mandi- 
bular bones,  whilst  behind,  it  is  continued  backwards  upon 
the  side  of  the  pharynx.  The  muscles  which  traverse  the 
fatty  layer  are  chiefly  the  zygomaticus  major,  the  risorius,  and 


Tip  of  tongue 
turned  up 


Ranine  vein 


Orifice  of 
Wharton's  duct 


Frenum  linguae 
Plica  fimbriata 

'Plica  sublingualis 


Fig.  135. — The  Sublingual  Region  in  the  Interior  of  the  Mouth. 


the  posterior  fibres  of  the  platysma.  The  parotid  duct  pierces 
the  three  inner  layers  of  the  cheek,  and  opens  into  the  vesti- 
bule of  the  mouth  opposite  the  second  molar  tooth  of  the 
upper  jaw. 

Gums  and  Teeth. — The  mucous  membrane  of  the  gums  is 
smooth,  vascular,  and  firmly  bound  down  to  the  subjacent 
periosteum  of  the  alveolar  portions  of  the  jaws  by  a  stratum 
of  dense  connective  tissue.  It  is  continuous  on  the  one 
hand  with  the  mucous  membrane  of  the  lips  and  cheeks, 
and  on  the  other  with  the  mucous  membrane  of  the  floor  of 
the  mouth.  The  gum  embraces  closely  the  neck  of  each 
tooth. 


MOUTH 


365 


In  the  adult  the  teeth  in  each  jaw  number  sixteen.  From 
the  middle  line  backwards,  on  each  side,  they  are  the  two 
incisors,  the  canine,  the  two  bicuspids,  the  three  molars. 

Floor  of  the  Mouth. — -The  mucous  membrane  is  reflected 
from  the  inner  aspect  of  the  lower  jaw,  on  to  the  side  of  the 
tongue,  but  in  the  fore-part  of  the  mouth  the  tongue  lies  more 
or  less  free  in  the  buccal  cavity.  Here  the  mucous  membrane 
stretches  across  the  floor  from  one  side  of  the  lower  jaw  to 
the  other.      On  each  side  of  this  region  the  projection  formed 


Uvula 

Posterior  pillar 

Tonsil 

Anterior  pillar  — 

Posterior  wall  of         _JM]ttl 
oral  pharynx  t^H^<|j5 

Tongue 


Fig.  136. — Isthmus  of  the  Fauces  as  seen  through  the 
widely  opened  Mouth.  The  tonsils  in  the  individual  from 
which  this  drawing  was  taken  were  somewhat  enlarged. 

by  the  sublingual  gland  can  be  distinguished.  Further,  if  the 
tongue  be  pulled  upwards,  a  mesial  fold  of  mucous  membrane 
will  be  seen  to  connect  its  under  surface  to  the  floor.  This 
is  the  frenum  linguce.  The  dissector  must  also  look  for  the 
openings  of  Wharton's  ducts.  Each  terminates  in  a  papillary 
orifice  placed  close  to  the  side  of  the  frenum.  Farther  back, 
between  the  side  of  the  tongue  and  the  jaw,  and  on  the 
summit  of  the  plica  sublingualis,  are  the  openings  of  the  ducts 
of  Rivinus. 

Roof  of  the  Mouth. — The  hard  and  the  soft  palate  form 
the  continuous  concave  and  vaulted  roof  of  the  mouth  (Fig. 


366  HEAD  AND  NECK 

138).  Projecting  from  the  middle  of  the  posterior  free  margin 
of  the  soft  palate,  and  resting  upon  the  dorsum  of  the  tongue, 
will  be  seen  the  uvula  (Fig.  136).  The  palate  both  hard  and 
soft  is  traversed  by  a  median  ridge  or  raphe  which  terminates 
in  front,  opposite  the  anterior  palatine  foramen,  in  a  slight 
elevation  or  papilla  termed  the  incisive  pad  ox  palatine  papilla. 
In  the  anterior  part  of  the  hard  palate  the  mucous  membrane 
on  each  side  of  the  raphe  is  thrown  into  three  or  four  trans- 
verse hard  corrugations  or  ridges ;  behind  this  it  is  compara- 
tively smooth. 

Isthmus  Faucium. — This  name  is  given  to  the  communi- 
cation between  the  buccal  cavity  and  the  pharynx  (Fig.  136). 
To  obtain  a  good  view  of  it  from  the  front,  the  mouth  must 
be  well  opened  and  the  tongue  depressed.  The  isthmus 
faucium  and  the  parts  which  bound  it  can  best  be  examined 
in  the  living  subject  (Fig.  136).  It  is  bounded  above  by  the 
soft  palate,  below  by  the  dorsum  of  the  tongue,  and  on  each 
side  by  two  curved  folds  of  mucous  membrane,  termed  re- 
spectively the  anterior  and  the  posterior  pillars  of  the 
fauces. 

The  pillars  of  the  fauces  spring  from  the  base  of  the  uvula, 
and  arch  outwards  and  then  downwards.  The  anterior  pillar 
(arcus  glossopalatinus)  as  it  descends  inclines  forwards,  and 
ends  upon  the  side  of  the  posterior  part  of  the  tongue ; 
the  posterior  pillar  (arcus  pharyngopalatinus),  more  strongly 
marked,  inclines  backwards,  and  is  lost  upon  the  side  of  the 
pharynx.  The  former  encloses  the  palato-glossus  muscle,  the 
latter  the  palato-pharyngeus  muscle. 

In  the  triangular  interval  which  is  formed  by  the  divergence 
of  these  two  folds  will  be  observed  the  tonsil. 

Strictly  speaking,  the  term  isthmus  fauciwn  should  be  con- 
fined to  the  interval  between  the  two  anterior  palatine  arches, 
as  the  tonsil  and  the  posterior  palatine  arches  belong  to  the 
lateral  wall  of  the  pharynx. 

Pharynx. — The  pharynx  is  a  wide  musculo-aponeurotic 
canal  about  5  inches  long,  which  extends  from  the  base  of 
the  cranium  to  the  level  of  the.  body  of  the  sixth  cervical 
vertebra.  Here  at  the  lower  border  of  the  cricoid  cartilage 
it  becomes  continuous  with  the  oesophagus.  Placed  behind 
the  nasal  cavities,  the  mouth  and  the  larynx,  it  serves  as  the 
passage  which  conducts  air  to  and  from  the  larynx,  as  well  as 
the  food  from  the  mouth  to  the  oesophagus. 


PHARYNX  367 

To  obtain  a  proper  idea  of  the  connexions  of  the  pharynx,  the  dissector 
should  moderately  distend  its  walls  by  stuffing  it  with  tow.  This  may  be 
introduced  either  from  above,  through  the  mouth,  or  from  below,  through 
the  oesophagus. 

The  pharynx  will  now  present  a  somewhat  ovoid  form.  It 
is  widest  opposite  the  hyoid  bone ;  from  this  upwards  it 
narrows  slightly  as  it  ascends  to  the  basis  cranii.  When 
traced  in  an  opposite  direction  its  width  diminishes  rapidly 
and  uniformly,  until  it  gives  place  to  the  oesophagus.  Pos- 
teriorly its  wall  is  complete,  and  when  in  position  rests  upon 
the  upper  five  cervical  vertebrae,  the  prevertebral  muscles,  and 
the  prevertebral  fascia.  To  these  it  is  bound  by  some  lax 
connective  tissue  which  offers  no  barrier  to  the  movements  of 
the  canal  during  the  process  of  deglutition.  Laterally  the 
pharynx  is  related  to  the  great  vessels  and  nerves  of  the  neck 
as  well  as  to  the  styloid  process  and  the  muscles  which  take 
origin  from  it.  Upon  this  aspect  of  the  pharynx  also  is 
placed  the  pharyngeal  plexus  of  nerves,  which  supplies  its 
walls  with  motor  and  sensory  twigs.  In  front  the  pharyngeal 
wall  is  interrupted  by  the  openings  of  the  nasal  chambers, 
mouth,  and  larynx,  and  it  is  from  the  structures  which  lie  in 
proximity  to  these  apertures  that  it  derives  its  principal 
attachments.  Thus  from  above  downwrards  it  is  fixed — (a) 
to  the  internal  pterygoid  plate ;  (b)  to  the  pterygo-maxillary 
ligament ;  (c)  to  the  side  of  the  tongue ;  (d)  to  the  inner 
aspect  of  the  mandible ;  (e)  to  the  hyoid  bone  ;  (/)  to  the 
thyroid  cartilage ;  Qf)  to  the  cricoid  cartilage.  Above,  it  is 
attached  to  the  basis  cranii.  These  various  attachments  will 
be  studied  more  fully  when  we  dissect  the  constituents  which 
enter  into  the  construction  of  its  wall. 

It  should  be  noted  that  an  altogether  false  idea  of  the 
natural  form  of  the  pharynx  is  obtained  when  it  is  examined 
in  its  present  stuffed  condition  and  apart  from  the  vertebral 
column,  against  which  it  rests.  When  seen  in  transverse 
sections  of  the  frozen  body  it  will  be  observed  that  with  the 
exception  of  its  upper  or  nasal  part,  which  remains  patent 
under  all  conditions,  the  anterior  wall  is  more  or  less  nearly 
approximated  to  the  posterior  wall,  and  below  the  opening  of 
the  larynx  it  presents  the  appearance  of  a  simple  transverse 
slit. 

Pharyngeal  Wall. — The  wall  of  the  pharynx  may  be  said 
to  consist  of  three  well-marked  strata — viz.,  an  external  mus- 


368  HEAD  AND  NECK 

cular,  an  intermediate  aponeurotic,  and  an  internal  mucous. 
The  muscular  layer,  which  is  composed  of  the  three  con- 
strictor muscles,  with  the  stylo-pharyngeus  and  palato- 
pharyngeus  on  each  side,  should  first  be  dissected. 

For  this  purpose,  place  the  preparation  so  that  the  chin  rests  upon  a 
block,  and  the  pharynx  hangs  downwards  with  its  posterior  surface 
towards  the  dissector.  The  constrictor  muscles  should  now  be  carefully 
cleaned  in  the  direction  of  the  muscular  fibres,  by  removing  the  bucco- 
pharyngeal fascia  which  covers  them. 

Bucco- pharyngeal  Fascia. — This  coating  is  sometimes 
spoken  of  under  the  name  of  the  tunica  pharyngis  externa  ; 
more  frequently,  however,  it  is  called  the  bucco-pharyngeal 
fascia,  seeing  that  it  is  continuous  in  front  with  the  buccal 
aponeurosis.  This  fascial  investment  must  not  be  con- 
founded with  the  prevertebral  layer  of  cervical  fascia  which 
forms  a  distinct  lamina  behind  it.  The  bucco-pharyngeal 
and  the  prevertebral  layers  of  fascia  are  separated  from  each 
other  by  an  interval  occupied  by  lax  connective  tissue,  and 
which,  from  the  ease  with  which  fluids  can  travel  within  it,  is 
called  the  retro-pharyngeal  space.  Both  layers  of  fascia  are 
connected  laterally  with  the  carotid  sheath. 

Pharyngeal  Veins. — Upon  the  posterior  and  lateral  walls 
of  the  pharynx  the  dissector  will  not  fail  to  notice  numerous 
veins  joined  together  in  a  plexiform  manner.  These  con- 
stitute the  pharyngeal  venous  plexus,  which  collects  blood 
from  the  pharynx,  soft  palate,  and  prevertebral  region,  and 
communicates  with  the  pterygoid  plexus.  Two  or  more 
channels  lead  the  blood  from  it  to  the  internal  jugular  vein. 
This  venous  plexus,  together  with  the  pharyngeal  plexus  of 
nerves,  will  require  to  be  removed  in  order  to  display  the 
muscles  properly. 

Constrictor  Muscles. — The  constrictor  muscles  are  three 
flat  sheets  of  muscular  fibres  which  are  so  arranged  that 
they  overlap  each  other  from  below  upwards ;  thus  the 
inferior  constrictor  overlaps  the  lower  part  of  the  middle 
constrictor,  whilst  the  middle  constrictor  in  turn  overlaps  the 
lower  part  of  the  superior  constrictor.  The  three  muscles 
are  inserted  in  the  mesial  plane  into  the  median  raphe,  which 
descends  from  the  basilar  process  of  the  occipital  bone  along 
the  posterior  aspect  of  the  pharynx. 

The  inferior  constrictor  (musculus  constrictor  pharyngis 
inferior)  (Fig.  137,  /)  is  narrow  in  front  at  its  origin,  but  it 


PHARYNX 


369 


spreads  out  as  it  passes  backwards  towards  its  insertion.  It 
arises  by  two  heads ;  of  these  the  lower  springs  from  the 
posterior  part  of  the  side  of  the  cricoid  cartilage,  whilst  the 
upper  and  larger  head  takes  origin  from  the  inferior  cornu, 
the  oblique  line   of  the   ala,   and  the  upper   border   of  the 


g> 

h. 
k. 
I. 


Buccinator. 
Tensor  palati. 
Levator  palati. 
Superior  constrictor. 
Middle  constrictor. 
Inferior  constrictor. 
Thyro-hyoid. 
Hyoglossus. 
Stylo-hyoid. 
Mylo-hyoid. 
Crico-thyroid. 
Stylo-pharyngeus. 
Stylo-glossus. 
Stylo-hyoid  ligament. 
Pterygo-maxillary  ligament. 
Glosso-pharyngeal  nerve. 
Superior  laryngeal  artery. 
Superior  laryngeal  nerve. 
External  laryngeal  nerve. 
Inferior  laryngeal  nerve  and 
artery. 


FlG.  137. — Profile  view  of  the  Pharynx  to  show  the  Constrictor 
Muscles.      (From  Turner.) 

thyroid  cartilage.  The  muscle  curves  backwards  round  the 
pharyngeal  wall  to  meet  its  fellow  of  the  opposite  side  in  the 
median  raphe.  The  lower  fibres  take  a  horizontal  direction, 
but  the  remainder  ascend  with  increasing  degrees  of  obliquity, 
until  the  highest  fibres  reach  the  raphe  at  a  point  a  short 
distance  below  the  basis  cranii.  The  lower  margin  of  the 
inferior  constrictor  overlaps  the  commencement  of  the 
(esophagus,  and  passing  upwards  under  cover  of  it,  so  as  to 
vol.  11 — 24 


37° 


HEAD  AND  NECK 


reach   the  larynx,  will  be  seen  the  recurrent  laryngeal  nerve 
and  the  laryngeal  branch  of  the  inferior  thyroid  artery. 

The  middle  constrictor  (musculus  constrictor  pharyngis 
medius)  is  a  fan-shaped  muscle  (Fig.  137,  e).  Narrow,  and 
pointed  in  front,  it  arises  from  the  great  and  small  cornua  of 
the  hyoid  bone  as  well  as  from  the  stylo-hyoid  ligament. 
From  this  its  fibres  radiate  widely,  and  pass  round  the 
pharyngeal  wall,  to  be  inserted  with  the  corresponding  fibres 
of  the  opposite  side  into  the  median  raphe.  The  lower 
portion  of  this  muscle  is  overlapped  by  the  inferior  constrictor, 
and  in  the  interval  which  separates  the  margins  of  the 
muscles  in  front,  the  internal  laryngeal  nerve  and  the 
laryngeal  branch  of  the  superior  thyroid  artery  will  be  seen 
piercing  the  thyro-hyoid  membrane  to  gain  the  interior  of  the 
larynx. 

Dissection. — The  superior  constrictor  possesses  a  somewhat  complicated 
origin,  and  to  bring  this  fully  into  view  it  will  be  necessary  to  cut  through 
the  internal  pterygoid  muscle  about  its  middle,  and  turn  the  upper  and 
lower  portions  aside.  In  doing  this,  be  careful  of  the  small  tensor  palati 
muscle  which  lies  immediately  subjacent  to  the  internal  pterygoid. 

The  superior  constrictor  (musculus  constrictor  pharyngis 
superior)  (Fig.  137,  d)  has  a  weak  but  continuous  line  of 
origin  from  the  following  parts — viz.,  (a)  the  lower  third  of 
the  posterior  border  of  the  internal  pterygoid  plate,  and  the 
hamular  process ;  (b)  the  pterygo-maxillary  ligament  which  is 
common  to  it,  and  the  buccinator  muscle;  (c)  the  posterior  end 
of  the  mylo-hyoid  ridge  on  the  inner  aspect  of  the  mandible ; 
(d)  the  mucous  membrane  of  the  mouth,  and  side  of  the 
tongue.  From  this  somewhat  extensive  origin,  the  fibres  curve 
backwards  to  reach  the  median  raphe,  whilst,  as  a  rule,  some 
of  the  highest  gain  a  distinct  insertion  into  the  pharyngeal 
tubercle,  on  the  under  surface  of  the  basi-occipital  bone. 

The  lower  part  of  the  superior  constrictor  is  overlapped 
by  the  middle  constrictor,  and  in  the  interval  between  the 
two  muscles  will  be  seen  the  stylo-pharyngeus  as  it  passes 
downwards  under  cover  of  the  middle  constrictor  (Fig.  137, 
n).  In  the  same  interval  will  be  seen  the  glossopharyngeal 
nerve.  The  upper  border  of  the  muscle  is  free  and  crescentic, 
and  it  falls  short  of  the  basis  cranii. 

Pterygo-maxillary  Ligament  (Fig.  137,  g). — This  is  a 
strong,  narrow,  tendinous  band,  which  extends  from  the 
hamular    process    of    the    internal    pterygoid    plate,    to    the 


PHARYNX  37i 

posterior  part  of  the  mylo-hyoid  ridge  of  the  mandible.  It 
acts  as  a  tendinous  bond  of  union  between  the  buccinator 
and  superior  constrictor  muscles,  and  its  connexions  can  be 
best  appreciated  by  introducing  the  finger  into  the  mouth 
and  pressing  outwards  along  its  course. 

Sinus  of  Morgagni. — This  name  is  applied  to  the  semi- 
lunar space  which  intervenes  between  the  upper  crescentic 
margin  of  the  superior  constrictor  and  the  basis  cranii. 
The  deficiency  in  the  muscular  wall  of  the  pharynx  at  this 
point  is  compensated  for  by  the  increased  strength  of  the 
pharyngeal  aponeurosis.  In  contact  with  the  outer  surface 
of  the  aponeurosis,  a  little  dissection  will  display  two  muscles 
belonging  to  the  soft  palate — viz.,  the  levator  palati  and  the 
tensor  palati  (Fig.  137,  c  and  b).  The  levator  is  rounded  and 
fleshy,  and  lies  behind  the  tensor,  which  is  flatter  and  more 
tendinous.  The  latter  can  readily  be  recognised,  from  its 
position  in  relation  to  the  deep  surface  of  the  internal 
pterygoid  muscle,  and  from  its  tendon  turning  inwards  under 
the  hamular  process.  In  the  upper  part  of  the  space,  close 
to  the  basis  cranii,  and  in  intimate  relationship  to  the  origin 
of  the  two  muscles,  will  be  seen  the  Eustachian  tube. 

Pharyngeal  Aponeurosis. — The  pharyngeal  aponeurosis  is 
strongly  marked  in  its  upper  part,  and  maintains  the  integrity 
of  the  wall  of  the  pharynx  where  the  muscular  fibres  are 
absent.  As  it  is  traced  downwards  it  gradually  becomes 
weaker,  until  it  is  ultimately  lost  as  a  distinct  layer.  It  lies 
between  the  muscles  and  mucous  membrane,  and  only  comes 
to  the  surface  where  the  muscles  are  absent.  It  is  the 
principal  means  by  which  the  pharynx  is  attached  to  the  base 
of  the  skull.  It  is  also  united  to  the  Eustachian  tubes  and 
the  bony  margins  of  the  posterior  nares. 

Dissection. — The  pharynx  should  now  be  opened  by  a  vertical  and 
mesial  incision  through  the  entire  length  of  the  posterior  wall.  At  the 
upper  extremity  of  this  cut,  the  knife  should  be  carried  transversely  out- 
wards, close  to  the  basis  cranii,  so  as  to  divide  the  attachment  of  the 
posterior  wall  to  the  basi-occipital  bone.  The  stuffing  should  be  removed 
and  the  mucous  surface  of  the  pharynx  cleansed. 

Interior  of  the  Pharynx. — The  mucous  membrane,  or  inner- 
most stratum  which  enters  into  the  construction  of  the 
pharyngeal  wall,  is  now  exposed,  and  it  should  be  observed 
that  it  is  continuous,  through  the  various  apertures  which 
open  into  the  pharynx,   with  the  mucous  membrane  of  the 


372 


HEAD  AND  NECK 


nasal  chambers,  of  the  Eustachian  tubes  and  tympanic  cavities, 
of  the  buccal  cavity,  of  the  larynx,  and  of  the  (esophagus. 

Race??wse  glands,  which  lie  immediately  subjacent  to  the 
mucous  membrane  and  which  secrete  mucus,  are  present  in 


Middle  turbinated  bone 
Middle  meatus 
Atrium 

Inferior 
turbinated  bone 
Inferior  meatus 

Vestibule  of 
nasal  cavity 


Soft  palate 


Anterior  pillar 
of  fauces 


Superior  meatus 

Recessus  spheno-ethmoidalis 
Sphenoidal  sinus 
Pituitary  body 

Pharyngeal  recess 
Pharyngeal  tonsil 

Eustachian  orifice 

Upper  surface 

of  soft  palate 

Salpingopharyngeal 

fold 

Posterior  pillar 

of  fauces 

Tonsil 


Pharyngeal  part 
of  tongue 


Genio-glossus 

Genio-hyoid 


Cartilage  of  epiglottis 


Thyroid  cartilage 


Epiglottis 

Cuneiform  tubercle 

Tubercle  of 
Santorini 

Laryngeal  sinus 
Cricoid  cartilage 


Fig.  138.— Sagittalsection  through  the  Nasal  Chamber,  the  Mouth,  Larynx, 
and  Pharynx,  a  little  to  the  right  of  the  mesial  plane. 

great  numbers.  There  are  also  numerous  lymphoid  follicles, 
and  in  certain  localities  these  are  aggregated  together  into 
large  masses  (the  tonsils  and  the  pharyngeal  tonsil),  which  will 
require  to  be  studied  with  the  section  of  the  pharynx  in 
relation  to  which  they  are  placed. 


PHARYNX  373 

The  soft  palate,  which  projects  backwards  into  the  pharynx 
behind  the  isthmus  faucium  like  a  curtain,  divides  the  cavity 
of  the  pharynx  into  an  upper  and  a  lower  part.  The  upper 
part,  called  the  naso-pharynx,  is  brought  into  communication 
with  the  nasal  chambers  and  the  tympanic  cavities  by  four 
apertures,  viz.,  the  two  choanal  or  posterior  nares  and  the 
mouths  of  the  two  Eustachian  tubes. 

The  lower  portion  of  the  pharynx  may  be  regarded  as 
consisting  of  an  oral  part,  which  lies  behind  the  mouth  and 
tongue,  and  a  laryngeal  part,  which  is  placed  behind  the 
larynx.  Below  the  soft  palate  there  are  three  mesial  open- 
ings into  the  pharynx,  viz.,  the  opening  of  the  7?iotcth  or  isthmus 
faucium,  the  ope?iing  of  the  larynx,  and  the  opening  of  the 
oesophagus. 

Naso-Pharynx  (pars  nasalis). — The  naso-pharynx  is  situated 
immediately  behind  the  nasal  chambers  and  below  the  body 
of  the  sphenoid  and  the  basilar  part  of  the  occipital  bone. 
It  is  the  widest  part  of  the  pharynx.  Its  walls  are  not  capable 
of  movement,  and  consequently  its  cavity  always  remains  patent, 
and  presents  under  all  conditions  very  much  the  same  form. 

The  front  wall  of  the  naso-pharynx  is  deficient.  Here  the 
posterior  nares  or  choance  open  directly  into  the  naso-pharynx. 
These  are  two  large  oval  apertures  which  constitute  the  com- 
munication between  the  nasal  fossae  and  the  pharynx.  They 
are  separated  from  each  other  by  the  thin  posterior  border  of 
the  vomer  bone.  The  vertical  diameter  of  each  opening 
measures  about  one  inch,  whilst  the  transverse  diameter  at 
its  widest  part  is  about  half  an  inch.  By  looking  through  the 
posterior  nares  a  partial  view  of  the  two  lower  meatuses  of 
the  nose  and  of  the  posterior  ends  of  the  middle  and  inferior 
turbinated  bones  may  be  obtained. 

On  the  lateral  wall  of  the  naso-pharynx,  on  each  side,  is 
seen  the  orifice  of  the  Eustachian  tube,  and  behind  this  the 
pharyngeal  recess.  The  Eustachian  orifice  (ostium  pharyngeum) 
is  placed  behind  the  lower  part  of  the  choana  at  a  level 
which  corresponds  closely  with  the  posterior  end  of  the 
inferior  turbinated  bone.  It  is  bounded  above  and  behind 
by  a  high  prominent  and  rounded  margin  termed  the  Eustachian 
cushion  (torus  tuberius),  which  is  altogether  deficient  below 
and  in  front.  A  fold  of  mucous  membrane,  termed  the  salpingo- 
pharyngeal fold,  descends  upon  the  lateral  wall  of  the  pharynx 
from  the  posterior  part  of  the  Eustachian  cushion.     As  this  is 


374  HEAD  AND  NECK 

traced  downwards  it  gradually  disappears.  The  prominent 
posterior  part  of  the  Eustachian  cushion  favours  very  materi- 
ally the  passage  of  the  Eustachian  catheter.1 

In  the  natural  condition  of  parts  there  is  a  deep  slit-like 
recess  on  the  lateral  wall  of  the  naso-pharynx  immediately 
behind  the  prominent  posterior  lip  of  the  Eustachian  orifice. 
This  is  termed  the  lateral  recess  of  the  pharynx,  or  the  fossa  of 
Rosenmilller,  and  it  possesses  considerable  interest  from  a 
developmental  point  of  view. 

The  roof  and  posterior  wall  of  the  naso-pharynx  are  not 
marked  off  from  each  other.  They  together  form  a  continuous 
curved  surface.  The  upper  portion  of  this  surface  looks 
downwards  and  may  be  regarded  as  the  roof;  the  lower  portion 
which  looks  forwards  constitutes  the  posterior  wall.  The  roof 
is  formed  by  the  basilar  part  of  the  occipital  bone,  and 
also  by  a  small  part  of  the  under  surface  of  the  basi-sphenoid 
covered  by  a  dense  periosteum  and  a  thick  coating  of  mucous 
membrane.  The  posterior  wall  is  supported  behind  by  the 
anterior  arch  of  the  atlas  and  the  odontoid  process  of  the 
axis  vertebra.  In  that  part  of  the  roof  which  stretches  across 
between  the  two  lateral  recesses  of  the  naso-pharynx  there  is  a 
marked  collection  of  lymphoid  tissue,  and  over  its  surface  the 
mucous  membrane  is  thickened  and  wrinkled.  This  is  the 
pharyngeal  tonsil,  and  in  its  lower  part  there  will  usually  be 
found  a  small  median  pit  termed  the  pharyngeal  bursa,  just 
large  enough  to  admit  the  point  of  a  fine  probe. 

The  floor  of  the  naso-pharynx  is  formed  by  the  curved, 
sloping  upper  surface  of  the  soft  palate.  Between  the  lower 
border  of  the  soft  palate  and  the  posterior  wall  of  the  pharynx 
there  is  an  interval  termed  the  pharyngeal  isthmus,  through 
which  the  naso-pharynx  communicates  with  the  oral  pharynx. 

It  is  important  to  note  that  the  posterior  wall  and  roof  of  the  naso- 
pharynx can  be  explored  by  the  finger,  introduced  through  the  mouth  and 
the  pharyngeal  isthmus. 

When  the  naso-pharynx  is  illuminated  by  a  mirror  introduced  through 
the  mouth,  a  view  of  the  four  orifices  which  open  into  this  part  of  the 
pharynx  may  be  obtained.  Owing  to  the  mirror  being  placed  obliquely 
and  below  the  level  of  the  hard  palate,  only  the  hinder  parts  of  the  inferior 
turbinated  bones  are  visible  through  the  choanoe,  and  the  inferior  meatus  of 
the  nose  is  altogether  out  of  sight.     The  middle  and  superior  meatuses  of 

1  A  Eustachian  catheter  can  be  very  readily  improvised  by  bending  the 
extremity  of  an  ordinary  blow-pipe.  The  dissector  is  recommended  to  practise 
the  passage  of  this  instrument  into  the  Eustachian  tube  through  the  nose. 


PHARYNX 


375 


the  nose,  and  the  middle  and  superior  turbinated  bones,  however,  can  be 
brought  into  view  and  their  condition  ascertained.  The  lateral  wall  of  the 
naso-pharynx  and  the  Eustachian  orifice  can  also  be  fully  inspected. 

Oral  Pharynx  (pars  oralis). — The  oral  pharynx  lies  behind 
the  tongue  and  mouth.  The  pharyngeal  part  of  the  tongue 
which  looks  more  or  less  directly  backwards  forms  its  anterior 
wall  in  its  lower  part.  Above  this  is  the  isthmus  of  the 
fauces,  or  the  opening  into  the  mouth,  limited  on  either  side 


Tongue 


Hyoid 


True  vocal  cord 


Kima  gIottidi> j I 

I 

Pynform  sinus_/_M 

Superior  cornu  /*; 
of  thyroid"^ 


Pharyngeal  wall 
(cut) 


Middle  glosso- 
epiglottidean 
ligament ' 

Vallecula 

Pharyngc- 
epiglottic  fold 

Epiglottis 

Cushion  of 
epiglottis 

Aryteno- 
id   epiglottidean  fold 
Laryngeal  sinus 

False  vocal  cord 
Cuneiform  cartilage 

Tubercle  of 
Santorini 


Posterior  aspect 
of  cricoid  cartilage 


FlG.   139. -—.Superior  Aperture  of  Larynx  exposed  by  laying  open 
the  pharynx  from  behind. 

by  the  anterior  pillar  of  the  fauces.  These  pillars  may  be 
regarded,  therefore,  as  giving  the  lateral  boundary  lines  between 
the  mouth  and  the  pharynx.  On  the  lateral  wall  of  the  oral 
pharynx  the  posterior  pillar  of  the  fauces  forms  a  prominent 
fold  which  is  gradually  lost  as  it  is  traced  downwards.  Within 
this  fold  is  the  palato-pharyngeus  muscle.  This  is  an  im- 
portant relation  when  it  is  remembered  that  the  posterior 
pillars  of  the  fauces  form  the  lateral  boundaries  of  the  pharyn- 
geal isthmus.  By  the  contraction  of  the  palatopharyngeal 
11     24  a 


376 


HEAD  AND  NEC* 


v 


muscles  the  two  posterior  pillars  can  be  approximated  so  as  to 
greatly  reduce  the  width  of  the  pharyngeal  isthmus. 

The  anterior  and  posterior  pillars  of  the  fauces  form  on 
each  lateral  wall  of  the  oral  pharynx  the  limits  of  a  triangular 
interval  in  which  is  lodged  the  tonsil.  The  upper  part  of  this 
area,  above  the  level  of  the  tonsil,  presents  a  small  depression 
termed  the  supra-tonsillar  fossa. 

Laryngeal  part  of  the  Pharynx  (pars  laryngea).  —  The 
portion  of  the  pharyngeal  cavity  which  lies  behind  the  larynx 
diminishes  rapidly  in  width  in  its  lower  part  so  as  to  bring 
its  lumen  into  conformity  with  that  of  the  oesophagus,  with 
which   it  is  continuous.      In  its  front  wall  from  above  down- 


Thyro-hyoid  membrane 
True  vocal  cord 
Processus  vocal  i 
Arytenoid  cartilage    ^sd^jk 
Platysma  w~*&A 

Posterior  wall 
of  pharynx 
Retropharyn-^  £ 
geal  space" 

Carotid  sheat 


Sterno-hyoid 
Thyro-hyoid 


Scalenus  anticu 

Longus  colli 


cartilage 

hyoid 

us  pyriformis 

Superior  thyroid 
Descendens 
hypoglossi 
Common  carotid 

AInternal  jugular 
Vagus 


Sympathetic  cord 


Vertebral  artery 

Fig.   140.— Transverse  section  through  the  Neck  at  the  level  of  upper 
part  of  Thyroid  Cartilage. 

wards  may  be  seen:  (1)  the  epiglottis;  (2)  the  superior 
aperture  of  the  larynx  with  the  pyriform  fossa  or  sinus  on 
either  side  ;  and  (3)  the  posterior  surfaces  of  the  arytenoid  and 
cricoid  cartilages,  covered  by  muscles  and  mucous  membrane. 
The  superior  aperture  of  the  larynx,  situated  below  the 
pharyngeal  part  of  the  tongue,  is  a  large  obliquely  placed 
opening  which  slopes  rapidly  from  above  downwards  and 
backwards.  Somewhat  triangular  in  outline,  the  basal  part  of 
the  opening,  placed  above  and  in  front,  is  formed  by  the  free 
border  of  the  epiglottis.  Behind,  the  opening  rapidly  narrows, 
and  finally  ends  in  the  interval  between  the  two  arytenoid 
cartilages.  The  sides  of  the  aperture  are  formed  by  two 
sharp  and  prominent  folds  of  mucous  membrane,  termed  the 
aryteno-epiglottidean  folds,   which   stretch    between   the   lateral 


PHARYNX  377 

margins  of  the  epiglottis  in  front  and  the  arytenoid  cartilages 
behind.  Two  small  nodules  of  cartilage  in  the  hinder  part  of 
the  aryteno-epiglottidean  fold  give  rise  to  two  rounded  emi- 
nences, called  respectively  the  cuneiform  tubercle  in  front  and 
the  tubercle  of  Santorini  behind. 

On  either  side  of  the  lower  part  of  the  laryngeal  opening 
there  is  a  small  three-sided  or  pyramidal  recess  or  depression, 
called  the  sinus  pyriformis.  On  the  outer  side  it  is  bounded 
by  the  posterior  part  of  the  ala  of  the  thyroid  cartilage ;  on 
the  inner  side  by  the  arytenoid  cartilage ;  whilst  its  hinder 
wall  is  formed  by  the  posterior  wall  of  the  pharynx  when  this 
is  in  place.  The  sinus  pyriformis  presents  a  wide  entrance 
which  looks  upwards,  but  it  rapidly  narrows  towards  the  bottom 
(Figs.  139  and  140),  and  it  is  important  to  the  surgeon  because 
it  is  in  this  little  pocket  that  foreign  bodies  introduced  into 
the  pharynx  are  most  liable  to  be  caught. 

Below  the  opening  of  the  larynx,  the  anterior  and  posterior 
walls  of. the  pharynx  are  always  closely  applied  to  each  other, 
except  during  the  passage  of  food. 

The  oesophageal  opening  is  placed  opposite  the  lower  border  of 
the  cricoid  cartilage.    This  is  the  narrowest  part  of  the  pharynx. 

Soft  Palate  (velum  palatinum). — The  soft  palate  is  a 
movable  curtain,  which  projects  downwards  and  backwards 
into  the  pharynx.  During  deglutition,  it  is  raised  so  as 
to  shut  off  the  upper  nasal  part  of  the  pharynx  from  the 
portion  below,  and  at  the  same  time  open  up  the  isthmus 
faucium.  In  front  it  is  attached  to  the  posterior  margin  of 
the  hard  palate ;  on  each  side  it  is  connected  with  the  lateral 
wall  of  the  pharynx  j  whilst  posteriorly  it  presents  a  free 
border.  From  the  centre  of  this  free  margin  the  conical 
elevation  termed  the  uvula  projects,  whilst  the  sharp  concave 
part  of  the  border  on  either  side  of  the  uvula  becomes  con- 
tinuous with  the  posterior  palatine  arch  which  descends  on 
the  side  wall  of  the  pharynx.  The  upper  surface  of  the  soft 
palate  is  convex  and  continuous  with  the  floor  of  the  nasal 
fossae ;  the  inferior  surface  is  concave  and  continuous  with  the 
vaulted  roof  of  the  mouth.  The  anterior  palatine  arch  curves 
outwards  from  this  surface  of  the  soft  palate  a  short  distance 
in  front  of  its  posterior  free  border.  Upon  the  inferior  surface 
may  be  seen  a  slightly  marked  mesial  ridge  or  raphe. 

The  soft  palate  is  composed  of  a  fold  of  mucous  membrane, 
between    the    two    layers   of   which   are    interposed    muscular, 


378  HEAD  AND  NECK 

aponeurotic,  and    glandular   structures,   together  with  blood- 
vessels and  nerves. 

r  The  two  levatores  palati. 
The  two  tensores  palati. 
Palatal  muscles,        .      <  The  two  palato-glossi. 

The  two  palato-pharyngei. 
I  The  azygos  uvulae. 
Palatal  aponeurosis. 
Palatal  glands. 

i  Ascending  palatine  from  facial. 
.    ,     •  !   Palatine  branch  from  ascending  pharyngeal. 

I  Twigs  from  the  descending  palatine  branch  of  the  internal 
I.      maxillary. 
Nerves  '   Small  posterior  palatine,         .  f  from   the  spheno-  palatine 

(  External  posterior  palatine,    .  I  ganglion. 

The  racemose  mucous  glands  in  the  soft  palate  form  a  very 
thick  and  continuous  layer  immediately  subjacent  to  the 
mucous  membrane  which  clothes  its  inferior  surface.  Close 
to  the  posterior  border  of  the  hard  palate  the  soft  palate  con- 
tains very  few  muscular  fibres,  and  here  it  is  chiefly  composed 
of  the  two  layers  of  mucous  membrane  enclosing  the  glands, 
and  above  these  the  palatal  aponeurosis. 

Dissection. — The  dissection  of  the  soft  palate  is  difficult,  and  it  is  only 
in  a  fresh  part  that  the  precise  relations  of  the  different  muscular  layers 
can  be  made  out.  Begin  by  rendering  it  tense  by  means  of  a  hook,  and 
then  remove  carefully  the  mucous  membrane  from  its  upper  and  lower 
surfaces,  and  also  from  the  anterior  and  posterior  pillars  of  the  fauces. 
The  latter  proceeding  will  expose  the  palato-glossus  and  the  palato- 
pharyngeus  muscles  on  each  side. 

Palato-glossus  (musculus  glosso-palatinus). — The  palato- 
glossus is  a  delicate  muscular  slip,  which  arises  from  the  side 
of  the  posterior  part  of  the  tongue,  and  curves  upwards  and 
inwards  to  reach  the  under  surface  of  the  soft  palate  above 
the  glandular  layer.  Here  its  fibres  spread  out,  and  become 
continuous  with  the  corresponding  fasciculi  of  the  opposite 
side.      It  forms  the  lowest  muscular  stratum  of  the  soft  palate. 

Palato-pharyngeus  (musculus  pharyngo-palatinus). — The 
palato-pharyngeus  forms  two  muscular  strata  in  the  soft  palate 
which  enclose  between  them  the  azygos  uvulae  and  the  levator 
palati  muscles.  The  upper  layer  is  very  weak,  and  confined 
to  the  posterior  part  of  the  velum.  It  constitutes  the  most 
superficial  muscular  stratum  on  this  aspect  of  the  palate,  and 
becomes  continuous  with  the  corresponding  portion  of  the 
muscle  of  the  opposite  side.  The  deeper  layer  takes  origin 
from  the  posterior  margin  of  the  palate  bone  and  from  the 


PHARYNX  379 

palatal  aponeurosis,  while  some  of  its  fibres  mingle  with  those 
of  the  corresponding  muscle  of  the  opposite  side.  Outside 
the  soft  palate  the  two  strata  come  together,  and  are  joined 
by  one  or  two  delicate  muscular  slips  which  spring  from  the 
lower  border  of  the  cartilage  of  the  Eustachian  tube.  These 
slips  are  sometimes  described  as  the  salpingo-pharyngeus  muscle. 
The  palato-pharyngeus  thus  formed  arches  downwards  and 
backwards  in  the  posterior  pillar  of  the  fauces,  and  spreads 
out  into  a  thin  sheet  of  fibres  in  the  wall  of  the  pharynx. 
Blending  to  some  extent  with  the  stylo-pharyngeus,  it  is  inserted 
into  the  superior  and  posterior  borders  of  the  thyroid  cartilage. 
Some  of  its  fibres,  however,  incline  backwards,  and  are 
inserted  into  the  pharyngeal  aponeurosis. 

Azygos  Uvulae  (musculus  uvulae). — This  delicate  muscle  is 
placed  on  the  upper  aspect  of  the  soft  palate,  and  posteriorly 
it  is  covered  by  the  superficial  fibres  of  the  palato-pharyngeus. 
These  must  be  removed  to  expose  it  fully.  It  consists  of  two 
minute  slips  which,  as  a  rule,  arise  from  the  posterior  nasal 
spine  of  the  hard  palate,  and  lie  one  on  either  side  of  the 
mesial  plane.  As  they  proceed  backwards  into  the  uvula  they 
unite  into  a  single  rounded  muscular  belly. 

Dissection. — The  levator  palati  muscle  has  already  been  seen  on  the 
outer  aspect  of  the  pharynx  in  the  sinus  of  Morgagni.  To  display  it  fully 
it  is  necessary  to  remove  the  wall  of  the  pharynx  between  the  Eustachian 
tube  above  and  the  upper  border  of  the  superior  constrictor  below,  and 
then  follow  its  fibres  into  the  soft  palate.  In  a  well-injected  subject  the 
dissector  will  observe  the  ascending  palatine  artery  in  relation  to  this 
muscle. 

Levator  Palati  (musculus  levator  veli  palatini). — The 
levator  palati  is  a  rounded  fleshy  muscle  which  arises  from 
the  lower  and  inner  border  of  the  cartilage  of  the  Eustachian 
tube,  and  from  the  rough  surface  on  the  under  aspect  of  the 
apex  of  the  petrous  bone  in  front  of  the  carotid  canal.  It 
passes  downwards  and  forwards,  crosses  the  upper  border  of 
the  superior  constrictor,  and  piercing  the  pharyngeal  aponeu- 
rosis enters  the  soft  palate.  Here  its  fibres  spread  out  below 
the  azygos  uvulae  and  above  the  anterior  or  deep  portion  of 
the  palato-pharyngeus.  In  front,  some  of  the  fibres  are 
inserted  into  the  palatal  aponeurosis;  but  behind  this,  the 
larger  proportion  of  the  fibres  become  continuous  with  the 
corresponding  fasciculi  of  the  opposite  side. 

Tensor  Palati  (musculus  tensor  veli  palatini). — This  little 


380  HEAD  AND  NECK 

muscle  lies  in  front  of  the  levator  palati.  It  is  flat  and  band- 
like, and  closely  applied  to  the  deep  surface  of  the  internal 
pterygoid  muscle.  It  arises  from  the  scaphoid  fossa  at  the 
root  of  the  internal  pterygoid  plate,  from  the  spine  of  the 
sphenoid,  and  from  the  outer  aspect  of  the  Eustachian  tube. 
It  descends  perpendicularly  and  ends  in  a  tendon  which  turns 
horizontally  inwards  under  the  hamular  process.  A  synovial 
bursa  facilitates  the  play  of  the  tendon  upon  the  bone.  In 
the  soft  palate  the  tendon  expands  below  the  deep  part  of 
the  palato-pharyngeus,  and  is  inserted  partly  into  the  trans- 
verse ridge  on  the  under  surface  of  the  horizontal  plate  of  the 
palate  bone,  and  partly  into  the  palatal  aponeurosis  with 
which  it  blends. 

Palatal  Aponeurosis. — The  palatal  aponeurosis  extends 
backwards  from  the  posterior  margin  of  the  hard  palate  to 
give  strength  and  support  to  the  soft  palate.  At  first  it  is 
strongly  marked,  but  it  very  soon  becomes  lost  as  it  is  traced 
back  into  the  soft  palate.  The  small  portion  of  the  soft 
palate  which  it  supports  contains  few  muscular  fibres,  and 
remains  always  more  or  less  horizontal  in  position.  The 
much  more  extensive  hinder  muscular  part  of  the  soft  palate 
constitutes  the  movable  sloping  portion.  The  tensor  palati 
operates  upon  the  anterior  aponeurotic  portion  of  the  soft 
palate. 

Vessels  and  Nerves  of  the  Soft  Palate. — The  inferior  or 
ascending  palatine  branch  of  the  facial  is,  as  a  rule,  the 
principal  artery  of  supply  to  the  soft  palate.  It  has  already 
been  traced  to  the  outer  wall  of  the  pharynx  (pp.  237  and 
309).  Here  it  is  seen  in  the  sinus  of  Morgagni,  in  relation 
to  the  levator  palati  muscle  which  it  accompanies  into  the 
soft  palate.  The  palatine  branch  of  the  ascending  pharyngeal 
artery  may  also  be  traced  into  the  soft  palate.  In  cases 
where  the  preceding  artery  is  small,  this  twig  will  be  found 
enlarged  so  as  to  take  its  place  (p.  310).  The  descending 
balati?ie  branch  of  the  internal  maxillary  artery  likewise  sends 
small  twigs  to  the  soft  palate  and  tonsil. 

Two  nerves  enter  the  soft  palate  from  Meckel's  ganglion — viz.,  the  small 
posterior  palatine  and  the  accessory  posterior  palatine  nei-ve.  It  would 
appear,  however,  that  they  do  not  supply  the  muscles,  but  are  distributed 
to  the  mucous  membrane.  The  levator  palati,  the  azygos  uvulae,  the 
palato-glossus,  and  the  palato-pharyngeus  are  supplied  by  twigs  from  the 
pharyngeal  branches  of  the  vagus,  which  convey  to  them  fibres  which  are 
originally  derived  from  the  accessory  part  of  the  spinal  accessory  {v.  p.  318) 


PHARYNX  381 

(W.  Aldren  Turner).  The  tensor  palati  is  probably  supplied  by  the 
branch  which  it  receives  from  the  otic  ganglion,  and  which  probably  leads 
to  it  fibres  which  originally  come  from  the  motor  part  of  the  trigeminal 
nerve. 

Tonsils  (tonsillar  palatini). — The  tonsils  are  two  prominent 
masses  of  lymphoid  tissue  placed  one  on  each  lateral  wall 
of  the  pharynx  in  the  triangular  interval  between  the  two 
palatine  arches  and  immediately  above  the  pharyngeal  part 
of  the  tongue.  The  phary?igeal  or  internal  surface  of  the 
tonsil  is  perforated  by  a  number  of  orifices  which  lead  into 
crypts  or  recesses  in  its  substance.  The  deep  or  external 
surface  is  embedded  in  the  pharyngeal  wall  and  is  supported 
by  the  superior  constrictor  muscle  of  the  pharynx.  It  is 
covered  by  a  layer  of  fibrous  tissue  which  forms  an  incomplete 
capsule  for  the  organ.  It  is  important  to  note  that  between 
the  tonsil  and  the  superior  constrictor  there  is  some  lax 
connective  tissue,  so  that  the  organ  can  be  pulled  forwards 
by  the  volsellum  without  dragging  the  wall  of  the  pharynx 
with  it. 

The  tonsils  have  a  rich  blood-supply.  They  derive  arterial 
twigs  from  the  tonsillar  and  inferior  palatine  branches  of  the 
facial,  the  descending  palatine  branch  of  the  internal  maxillary, 
the  ascending  pharyngeal,  and  the  dorsalis  linguae. 

Eustachian  Tube  (tuba  auditiva). — This  is  the  canal  which 
conveys  air  from  the  pharynx  to  the  tympanic  cavity.  It  is 
divided  into  two  portions,  according  to  the  parts  which  enter 
into  the  construction  of  its  wall.  Thus,  in  the  outer  part  of 
its  course  as  it  nears  the  tympanum,  its  wall  is  bony,  and 
it  runs  in  the  interval  between  the  squamous  and  petrous 
portions  of  the  temporal  bone.  The  inner  part  is  placed  on 
the  base  of  the  skull,  and  is  lodged  in  the  gutter  or  groove 
between  the  apex  of  the  petrous  part  of  the  temporal  bone 
and  the  great  wing  of  the  sphenoid.  This  is  the  subdivision 
of  the  tube  which  comes  under  the  notice  of  the  dissector  at 
the  present  stage,  and  he  should  first  note  its  direction  and 
then  study  its  relations  and  the  construction  of  its  wall. 

The  direction  of  the  canal  can  be  readily  ascertained  by 
passing  a  probe  into  it  through  its  pharyngeal  orifice.  It  will 
be  seen  to  run  backwards  and  outwards  with  a  slight  inclina- 
tion upwards.  At  the  same  time  it  will  be  noticed  to  pass 
between  the  origin  of  the  levator  palati,  which  lies  upon  its 
inner  side,  and  the  origin  of  the  tensor  palati,  which  is  placed 


382  HEAD  AND  NECK 

upon  its  outer  side.  This  relationship  is  best  seen  in  coronal 
sections  through  the  frozen  head.  The  dissector  should  now 
proceed  to  remove  the  mucous  membrane  from  around  the 
pharyngeal  orifice  of  the  tube.  This  will  reveal  the  fact  that 
its  wall  is  strengthened  by  a  triangular  plate  of  cartilage, 
which  is  folded  upon  itself  so  as  to  protect  the  tube  on  its 
upper  and  inner  aspects.  The  cartilage  is  deficient  below 
and  externally,  its  place  being  taken  by  dense  fibrous  tissue, 
which  connects  the  margins  of  the  cartilage  and  completes 
the  wall  of  the  canal.  The  projecting  free  margin  of  the 
cartilage  gives  rise  to  the  Eustachian  cushion  already  ex- 
amined on  the  lateral  wall  of  the  naso-pharynx  (p.  373).  A 
muscular  slip,  which  descends  from  the  outer  margin  of  the 
cartilage  in  relation  to  the  outer  unprotected  side  of  the  tube, 
has  been  termed  the  dilatator  tuba  (Rudinger).  It  joins  the 
tensor  palati.  The  interior  of  the  tube  is  lined  by  mucous 
membrane  continuous  with  that  of  the  pharynx,  and  its 
calibre  is  very  different  in  different  parts  of  its  course.  It 
is  narrowest  at  a  point  termed  the  isthmus,  situated  at  the 
junction  of  the  osseous  and  cartilaginous  parts.  As  the  tube 
is  traced  from  this  to  the  pharynx  it  gradually  increases  in 
calibre,  and  attains  its  greatest  width  at  its  opening  into  the 
nasal  pharynx. 


CAROTID  CANAL. 

The  carotid  canal,  which  traverses  the  fore -part  of  the 
petrous  bone,  contains  the  internal  carotid  artery  and  the 
upward  continuation  of  the  cervical  sympathetic. 

Dissection. — The  carotid  canal  may  be  opened  up  by  removing  its 
inferior  wall  with  the  bone  pliers.  In  doing  this,  it  is  not  necessary  to 
interfere  with  the  Eustachian  tube,  which  lies  in  close  proximity.  It  is 
well  to  preserve  this  structure  until  we  undertake  the  dissection  of  the  otic 
ganglion. 

Internal  Carotid  Artery. — The  internal  carotid  artery  in 
this  part  of  its  course  is  about  three-fourths  of  an  inch  long. 
At  first  it  ascends  vertically ;  then,  bending  suddenly,  it  runs 
horizontally  forwards  and  inwards.  It  emerges  from  the 
canal  at  the  apex  of  the  petrous  bone,  and  enters  the  cranial 
cavity  by  piercing  the  external  layer  of  the  dura  mater.  From 
this    point    onwards    the    internal    carotid    artery    has    been 


CAROTID  CANAL  3§3 

already  examined  (p.  328).  Whilst  within  the  carotid  canal 
it  lies  in  front  of  and  below  the  cochlea  and  the  tympanum. 
The  Gasserian  ganglion  is  placed  above  it,  and  separated  from 
it  by  a  thin  plate  of  bone,  which  is  sometimes  absent. 

Ascending  Part  of  the  Cervical  Sympathetic. — The 
dissector  has  already  noted  a  large  branch  proceeding  from 
the  upper  end  of  the  superior  cervical  ganglion  and  entering 
the  carotid  canal  with  the  internal  carotid  artery.  This  almost 
immediately  divides  into  two  parts,  which  place  themselves 
one  on  either  side  of  the  artery,  and  supply  branches  to  its 
coats.  The  further  dissection  of  these  branches  is  a  matter 
of  some  difficulty,  and  can  only  be  satisfactorily  effected 
under  specially  favourable  circumstances.  The  external  branch 
breaks  up  into  the  carotid  plexus ;  the  internal  branch  is  con- 
tinued into  the  cavernous  plexus.  From  these  primary  off- 
shoots secondary  plexuses  are  prolonged  upon  the  various 
branches  which  spring  from  the  internal  carotid  artery. 

The  carotid  plexus,  which  lies  upon  the  outer  aspect  of  the  internal 
carotid  artery,  gives  off  the  following  branches— (1)  one  or  two  filaments 
to  the  abducent  or  sixth  nerve  as  it  turns  round  the  internal  carotid 
artery  ;  (2)  one  or  two  twigs  which  join  the  inner  part  of  the  Gasserian 
ganglion ;  (3)  the  large  deep  petrosal  nerve ;  (4)  the  small  carotico- 
tympanic nerve. 

The  large  deep  petrosal  nerve  runs  to  the  posterior  aspect  of  the  body  of 
the  sphenoid,  and  at  the  entrance  to  the  Vidian  canal  it  joins  the  great 
supe)-Jicial petrosal  nerve  and  forms  the  Vidian  nerve  (p.  329). 

The  carotico-tym panic  branch  of  the  carotid  plexus  joins  the  tympanic 
branch  of  the  glosso-pharyngeal  as  it  traverses  the  tympanum  (p.  315). 

The  carotid  plexus  also  receives  the  small  deep  petrosal  nei-ve  from  the 
tympanic  branch  of  the  glosso-pharyngeal. 

The  cavernous  plexus  has  already  been  sufficiently  described  on  p.  329. 


SUPERIOR  MAXILLARY  NERVE. 

As  the  superior  maxillary  nerve  proceeds  forwards  from  the 
Gasserian  ganglion  to  reach  the  face,  it  traverses  the  upper 
part  of  the  spheno-maxillary  fossa  and  the  infra-orbital  canal. 
The  dissector  should  therefore  proceed  to  expose  the  nerve  in 
these  localities. 

Dissection. — Remove  the  temporal  muscle  and  the  upper  head  of  the 
external  pterygoid  muscle,  and,  placing  the  saw  upon  the  cut  margin  of  the 
skull  at  a  point  immediately  above  the  external  auditory  meatus,  carry  it 
obliquely  downwards  and  forwards  through  the  squamous  part  of  the 
temporal  hour  mid  the  great  wing  of  the  sphenoid  towards  the  inner  end  of 
the  sphenoidal  fissure.     This  saw-cut  should  enter  the  sphenoidal  fissure 


3^4 


HEAD  AND  NECK 


immediately  to  the  outer  side  of  the  foramen  rotundum.  A  second  saw- 
cut  should  then  be  made  from  the  cut  margin  of  the  cranial  wall,  immedi- 
ately above  the  anterior  margin  of  the  great  wing  of  the  sphenoid  bone, 
downwards  into  the  sphenoidal  fissure  to  meet  the  first  saw-cut.  The 
wedge-shaped  piece  of  bone  included  between  these  cuts  can  now  be 
removed.  Additional  space  may  be  obtained  and  the  spheno -maxillary 
fossa  more  fully  opened  up  by  removing  what  remains  of  the  great  wing 
of  the  sphenoid  upon  the  outer  side  of  the  foramen  rotundum,  but  the 
circumference  of  this  aperture  must  be  carefully  preserved.  Proceed,  in  the 
next  place,  to  open  up  the  infra-orbital  canal.  In  its  posterior  part  its 
upper  wall  is  usually  so  thin  that  it  can  easily  be  removed  by  one  of  the 
blades  of  a  pair  of  forceps,  but  in  front  it  sinks  deeply  under  the  lower 
part  of  the  rim  of  the  orbital  opening,  and  here  the  chisel  must  be  em- 
ployed. The  superior  maxillary  nerve  can  now  be  defined  and  its 
branches  displayed.  The  infra-orbital  artery  and  vein,  which  accompany 
the  nerve,  will  be  exposed  at  the  same  time. 


Sphenopalatine 
ganglion 


Fig.  141. — Diagram  of  the  Superior  Maxillary  Nerve. 

Superior  Maxillary  Nerve  (nervus  maxillaris).  —  The 
superior  maxillary  nerve  springs  from  the  Gasserian  ganglion 
within  the  cranial  cavity  (p.  326).  It  is  composed  entirely  of 
sensory  fibres,  and  proceeds  forwards  under  the  dura  mater 
and  in  relation  to  the  lower  part  of  the  cavernous  sinus  to  the 
foramen  rotundum,  through  which  it  passes  into  the  spheno- 
maxillary fossa.  The  nerve  is  now  carried  across  the  upper 
part  of  this  fossa  and  enters  the  infra-orbital  canal,  where  it 
receives  the  name  of  infra-orbital  The  infra -orbital  canal 
traverses  the  floor  of  the  orbit,  which  also,  it  should  be 
remembered,  forms  the  roof  of  the  antrum  of  Highmore. 
Finally  the  nerve  emerges  upon  the  face  through  the  infra- 
orbital foramen,  and  breaks  up,  under  cover  of  the  levator 
labii  superioris,  into  numerous  branches,  which  form  a  dense 


SUPERIOR  MAXILLARY  NERVE  385 

plexus  with  twigs  from  the  facial  nerve.  Its  terminal  filaments 
are  distributed  to  the  lower  eyelid,  the  nose,  and  the  upper 
lip.  From  its  origin  within  the  cranium  to  its  termination  on 
the  face,  the  superior  maxillary  nerve  pursues  a  nearly  straight 
course,  and  in  each  stage  it  gives  off  one  or  more  branches. 
These  are : — 

1.  Within  the  cranium,    {Recurrent  (already  described,  p.  327). 

[  Orbital    or     temporo  -  malar    (already    de- 

2.  In  the  spheno-maxil-J  scribed,  p.  347). 

lary  fossa,     .  .     |  Spheno-palatine. 

I  Posterior  superior  dental. 

3.  In  the  infra-orbital     /Middle  superior  dental. 

canal,.         .  .    ( Anterior  superior  dental. 

(  Palpebral,  \ 

4.  In  the  face,     .         .    -J  Nasal,  V-  already  described,  p.  266. 

(_  Labial,        ) 

The  temporo-malar  nerve,  which  has  already  been  dissected 
in  the  orbit,  can  now  be  traced  back  to  its  origin  from  the 
superior  maxillary  nerve  in  the  spheno-maxillary  fossa.  The 
sphe?io-palatine  branches  are  two  stout  twigs  which  arise  from 
the  under  aspect  of  the  superior  maxillary  nerve,  and  proceed 
vertically  downwards  in  the  spheno-maxillary  fossa  to  Meckel's 
ganglion,  of  which  they  constitute  the  sensory  roots. 

Superior  Dental  Nerves  (nervi  alveolares  superiores). — 
These  are  usually  three  in  number,  and  are  distinguished  as 
posterior,  middle,  and  anterior.  The  middle  superior  dental 
nerve  is  sometimes  absent  as  a  separate  trunk,  in  which  case 
it  arises  in  common  with  the  anterior  superior  dental. 

The  posterior  superior  dental  nerve  takes  origin  in  the 
spheno-maxillary  fossa,  and  almost  immediately  divides  into 
two  branches,  which  proceed  downwards  upon  the  posterior 
aspect  of  the  body  of  the  superior  maxillary  bone.  They 
contribute  a  few  fine  filaments  to  the  mucous  membrane  of 
the  cheek  and  to  the  gum,  and  then  disappear  into  the 
minute  posterior  dental  foramina  to  supply  the  three  molar 
teeth  and  the  lining  membrane  of  the  antrum  of  Highmore. 

The  ?niddle  superior  dental  nerve  supplies  the  two  bicuspid 
teeth.  It  arises  from  the  infra-orbital  nerve,  a  short  distance 
in  front  of  the  spheno-maxillary  fossa,  and  can  be  easily 
detected  (when  present)  by  gently  raising  the  parent  trunk 
from  the  floor  of  the  canal.  It  descends  in  a  minute  canal 
which  traverses  the  outer  wall  of  the  antrum  of  Highmore. 

The  anterior  superior  dental  nerve,  much  the  largest  of  the 

vol..  n-25 


386  HEAD  AND  NECK 

three  dental  branches,  springs  from  the  infra- orbital  as  it 
approaches  the  fore-part  of  the  canal.  It  can  be  brought  into 
view  by  raising  the  parent  trunk  from  the  floor  of  the  canal, 
and  it  will  then  be  seen  to  enter  a  special  bony  tunnel  which 
traverses  the  upper  jaw  in  front  of  the  antrum  of  Highmore. 
The  dissector  should  endeavour  to  open  up  this  canal  with  the 
chisel.  After  supplying  a  branch  to  the  mucous  membrane 
of  the  lower  and  fore  part  of  the  nasal  fossa,  the  anterior 
superior  dental  nerve  divides  into  branches  for  the  incisor 
and  the  canine  teeth. 

While  traversing  the  upper  jaw,  the  three  superior  dental  branches 
communicate  with  each  other,  and  form  two  nerve-loops.  Numerous  twigs 
proceed  from  these,  and  join  in  a  fine  plexus.  It  is  from  this  plexus  that 
the  terminal  filaments  to  the  teeth  and  gum  take  origin. 

Infra-orbital  Artery  (arteria  infra-orbitalis). — The  infra- 
orbital artery  is  a  branch  of  the  internal  maxillary.  It  arises 
in  the  spheno-maxillary  fossa,  and  accompanies  the  infra-orbital 
nerve.  In  the  face  its  terminal  twigs  anastomose  with  branches 
of  the  facial,  transverse  facial,  and  buccal  arteries  ;  in  the 
infra-orbital  canal  it  gives  some  fine  branches  to  the  contents 
of  the  orbital  cavity,  and  also  the  anterior  dental  artery  (arteria 
alveolaris  superior  anterior),  which  accompanies  the  nerve  of 
that  name,  and  supplies  the  incisor  and  canine  teeth,  and  the 
lining  membrane  of  the  antrum. 

The  infra-orbital  vein  joins  the  pterygoid  plexus. 


OTIC  GANGLION— NASAL  FOSS^. 

Dissection. — The  portion  of  the  lower  jaw  which  still  remains,  together 
with  the  tongue  and  larynx,  must  now  be  removed  from  the  upper  part  of 
the  skull.  From  the  angle  of  the  mouth  on  each  side  carry  the  knife 
backwards  through  the  buccinator  and  mucous  membrane  of  the  cheek, 
the  pterygo-maxillary  ligament,  and  the  lateral  wall  of  the  pharynx.  The 
internal  pterygoid  muscle  has  already  been  divided,  but  it  will  be  necessary 
to  cut  the  internal  carotid  artery,  with  the  vessels  and  nerves  which  still 
connect  the  pharynx  with  the  skull.  The  larynx  and  tongue  may  be  laid 
aside  for  future  dissection. 

The  fore-part  of  the  skull  should  next  be  divided  into  two  lateral  parts 
by  sawing  it  through  in  the  sagittal  direction  close  to  one  side  of  the  nasal 
septum.  As  a  general  rule  the  nasal  septum  is  not  vertical,  but  deviates 
more  or  less  to  one  or  other  side  of  the  mesial  plane.  This  deviation  is 
more  frequently  directed  to  the  right  than  to  the  left  side.  Endeavour  to 
determine  the  direction  which  it  takes  in  the  skull  under  observation  by 
passing  a  probe  into  the  nasal  fossae  through  the  posterior  nares.     The 


OTIC  GANGLION  387 

section  through  the  skull  should  be  made  close  to  the  concave  side  of  the 
septum.  Begin  in  front  by  introducing  a  knife  into  the  nostril  of  that  side, 
and  carry  it  upwards  through  the  cartilaginous  part  of  the  nose  to  the  nasal 
bone.  Then  place  the  specimen  so  that  the  face  rests  upon  the  table,  and 
divide  the  soft  palate  from  before  backwards  in  the  same  plane.  The 
section  may  now  be  completed  by  sawing  from  behind  forwards  through 
the  hard  palate  and  bony  roof  of  the  nasal  fossa.  The  dissector  should 
make  every  effort  to  preserve  the  septum  of  the  nose  intact.  As  a  general 
rule  the  upper  turbinated  bone  is  partially  injured.  This  is  not  a  very 
serious  matter,  as  the  outer  aspect  of  the  nasal  fossa  can  be  studied  upon 
the  opposite  side  when  the  septum  of  the  nose  has  been  removed. 

If  the  part  has  been  well  preserved,  the  dissector  should  be  able  at  this 
stage  to  expose  the  otic  ganglion,  and  perhaps  also  some  of  its  more 
important  connexions.  Turn  the  specimen  so  that  its  inner  surface  looks 
upwards,  and,  carefully  detaching  the  levator  palati  from  its  origin,  throw 
it  downwards.  Then  remove  the  cartilaginous  part  of  the  Eustachian  tube. 
In  doing  this,  the  dissector  must  proceed  with  the  greatest  caution,  because 
the  ganglion  lies  immediately  subjacent.  By  following  the  nerve  to  the 
internal  pterygoid  muscle  upwards  and  backwards  to  its  origin  the  otic 
ganglion  will  be  discovered. 

Otic  Ganglion  (ganglion  oticum). — This  is  a  minute  oval 
body  about  4  mm.  in  length.  It  is  placed  immediately  below 
the  foramen  ovale,  between  the  deep  surface  of  the  inferior 
maxillary  nerve  and  the  tensor  palati  which  separates  it  from 
the  cartilaginous  part  of  the  Eustachian  tube.  The  middle 
meningeal  artery  lies  behind  it,  and  it  lies  in  the  most 
intimate  relationship  to  the  origin  of  the  nerve  to  the  internal 
pterygoid  muscle. 

The  otic  ganglion  is  usually  described  as  receiving  motor,  sensory,  and 
sympathetic  roots.  The  motor  root  is  supplied  by  the  nerve  to  the  internal 
pterygoid  muscle  ;  the  sympathetic  root  comes  from  the  plexus  around  the 
middle  meningeal  artery.  In  addition  to  these,  the  small  superficial  petrosal 
newe  enters  the  posterior  border  of  the  ganglion,  and  conveys  to  it  sensory 
fibres  from  the  glossopharyngeal  nerve  (p.  314). 

The  following  are  the  branches  which  proceed  from  the  otic  ganglion  : — 

C  A  twig  which   passes  downwards  and  forwards  to  the 

Branches  of  tensor  palati. 

distribution.     |  A  twig    which    proceeds   upwards    and    backwards    to 

V.  supply  the  tensor  tympani. 

(  One  or  more  fine  filaments  to  one  or  both  of  the  roots 

Connecting  of  the  auriculo-temporal  nerve, 

branches.         1   A  minute    communicating     filament     to    the    chorda 

\  tympani. 

Nasal  Septum  (septum  nasi). — The  nasal  septum  divides 
the  cavity  of  the  nose  into  two  narrow  chambers — the  right 
and  left  nasal  fossae.  It  is  not  placed  accurately  in  the  mesial 
plane,  but  almost  invariably  shows  a  bulging  or  deviation  to 
one  or  other  side  (more  frequently  to  the  right  side),  so  as  to 
reduce  the  width  of  one  fossa,  and  increase  the  capacity  of 


388 


HEAD  AND  NFXK 


the  other.  Immediately  above  the  orifice  of  the  nostril, 
or  the  anterior  aperture  of  the  nasal  fossa,  the  septum 
shows  a  slight  depression,  which  corresponds  to  the  vestibule 
of  the  nose,  and  forms  the  inner  wall  of  this  subdivision 
of  the  nasal  chamber.  The  vestibular  part  of  the  partition 
is  clothed  by  skin,  continuous  with  the  external  integument ; 
from  this  a  number  of  stiff  hairs,  termed  vibrissa,  project. 
Over   the  rest   of   its    extent    the    septum    nasi    is    covered 


Frontal  sinus 


Nasal  bone 


Vestibule  of^ 
nasal  chamber 

Opening  of 
Jacobson's  organ 


Sublingual  gland 
Mandible 


Septal  cartilage 
Mes-ethmoid 

Vomer 


Sphenoidal  air  sinus 

% 

IKM  Eustachian  cushion 

\^»*'i ?,'L. Eustachian  opening 

VAi'r  Pharyngeal  recess 
Pharyngeal  tonsil 

_l  Atlas 

-V^/l  Soft  palate 
iv^Z— Transverse  ligament 
WM—  Axis  vertebra 

«"$ — Epiglottis 

Hyoid  bone 


Fig.  142. — Antero-posterior  section  through  the  Nose,  Mouth,  and 
Pharynx,  a  little  to  the  left  of  the  mesial  plane. 

with  mucous  membrane,  and  presents  two  districts,  viz., 
a  lower  or  respiratory  area,  and  a  much  smaller  upper 
or  olfactory  area,  comprising  not  more  than  the  upper 
third  of  the  septum  in  which  the  branches  of  the  olfactory 
nerve  spread  out.  The  respiratory  mucous  membrane  is  very 
thick  and  spongy.  It  is  highly  vascular,  and  contains  numerous 
racemose  glands.  The  minute  orifices  of  the  gland  ducts 
can  be  detected  by  the  naked  eye.  Over  the  olfactory  district 
of  the  septum,  the  mucous  membrane  is  softer  and  more 
delicate,  and  not  so  thick.  In  the  fresh  state  it  presents  a 
yellowish  colour,  and  the  glands  are  smaller. 


NASAL  FOSSAE  389 

In  favourable  cases  a  minute  orifice  may  be  detected  in  the  mucous 
membrane  on  the  lower  and  fore  part  of  the  nasal  septum  immediately 
behind  the  vestibular  area.  It  is  placed  above  the  anterior  end  of  a 
well-marked  elongated  projection  which  passes  obliquely  backwards  and 
upwards,  and  corresponds  to  the  thickened  lower  margin  of  the  septal 
cartilage.  This  aperture  varies  in  diameter  from  \  mm.  to  \\  mm. 
(Schwalbe).  It  leads  into  a  narrow  canal,  which  passes  backwards  for 
a  short  distance,  and  then  ends  blindly.  It  is  of  interest  because  it 
represents  in  the  human  subject  the  rudiment  of  the  organ  of  Jacobson, 
a  tubular  structure  which  is  highly  developed  in  some  of  the  lower  animals. 

Construction  of  the  Nasal  Septum. — Strip  the  mucous 
membrane  from  the  exposed  surface  of  the  septum  nasi.  By 
this  proceeding  the  intimate  connexion  which  exists  between 
the  mucous  membrane  and  the  subjacent  periosteum  and 
perichondrium  will  become  apparent,  and  the  parts  forming 
the  septum  will  be  rendered  visible.  The  bulk  of  the  partition 
is  composed  of  the  perpendicular  plate  of  the  ethmoid  and 
the  vomer  posteriorly,  and  of  the  septal  cartilage  in  front. 
Small  portions  of  other  bones  take  a  minor  part  in  its  con- 
struction. Thus,  above  and  behind  there  are  the  crest  and 
rostrum  of  the  sphenoid  \  above  and  in  front  is  the  nasal 
spine  of  the  frontal  bone ;  whilst  below  there  is  the  crest  of 
bone  formed  by  the  apposition  of  the  palatal  processes  of  the 
palate  and  superior  maxillary  bones  of  opposite  sides. 

The  septal  cartilage  (cartilago  septi  nasi)  fills  up  the  wide 
angular  gap  which  intervenes  between  the  perpendicular  plate 
of  the  ethmoid  and  the  vomer,  and  it  projects  forwards  towards 
the  point  of  the  nose.  It  is  a  broad  irregularly  quadrilateral 
cartilaginous  plate.  Its  upper  and  posterior  border  is  in  ap- 
position with  the  fore  border  of  the  mes-ethmoid ;  its  lower 
and  posterior  border,  much  thickened,  is  received  into  the 
groove  in  the  fore  border  of  the  vomer  and  the  incisor  crest 
of  the  maxillary  bones.  The  angle  between  these  two  borders 
is  prolonged  backwards  for  a  varying  distance  in  the  form  of 
a  tongue -shaped  cartilaginous  process,  which  occupies  the 
interval  between  the  two  plates  of  the  vomer.  The  upper  and 
anterior  border  of  the  septal  cartilage  is  in  contact  above  with 
the  suture  between  the  two  nasal  bones  ;  below  this  it  is 
related  to  the  two  lateral  cartilages  of  the  nose,  whilst  still 
lower  down  it  is  seen  in  the  interval  between  the  two  cartilages 
of  the  nasal  aperture  Its  connexion  with  the  lateral  cartilage 
of  each  side  is  a  very  intimate  one;  indeed,  below  the  nasal 
bones  the  three  cartilages  are  directly  continuous,  but  lower 
down  they  are  separated  by  a  fissure  which  runs  upwards  for 


39°  HEAD  AND  NECK 

some  distance  on  each  side.  The  lower  and  anterior  border  is 
very  short ;  it  is  free,  and  extends  backwards  to  the  anterior 
nasal  spine.  The  anterior  angle  of  the  septal  cartilage  is  blunt 
and  rounded,  and  does  not  reach  to  the  point  of  the  nose, 
which  is  thus  formed  by  the  cartilages  of  the  aperture  (p.  279). 
The  deviation  of  the  septum  nasi  from  the  mesial  plane 
will  now  (in  all  probability)  be  seen  to  be  due  to  a  bulging 
to  one  side  of  the  vomer  and  mes-ethmoid  along  their  line 
of  union.  It  is  not  developed  until  after  the  seventh  year 
of  life. 

Dissection. — The  septal  cartilage  and  thin  bony  lamina?  must  now  be 
removed  piecemeal.  This  must  be  done  very  carefully,  as  it  is  necessary 
to  preserve  intact  the  mucous  membrane  which  clothes  the  opposite  side 
of  the  septum.  It  is  in  this  that  the  nerves  and  blood  vessels  must  be 
examined. 

Vessels  and  Nerves  of  the  Septum  Nasi. — The  following 
is  a  list  of  the  nerves  : — 

Nerves  of  Smell,       .  Olfactory. 

(  1.   Naso-palatine. 


Nerves  of  Common  |  2.   Septal  branch  of  the  nasal  nerve  proper. 

Sensation,     .  .  13.   Nasal  branches  from   Meckel's  ganglion 

V.  and  from  the  Vidian  nerve. 

The  inner  group  of  olfactory  nerves  which  are  distributed  in 
the  mucous  membrane  of  the  upper  part  of  the  nasal  septum 
are  barely  distinguishable,  except  in  a  fresh  part ;  further, 
they  are  so  soft,  that  it  is  hardly  possible  to  isolate  them. 
They  enter  the  nasal  fossa  through  the  inner  series  of  apertures 
in  the  cribriform  plate  of  the  ethmoid,  and  proceed  down- 
wards in  grooves  on  the  surface  of  the  perpendicular  plate  of 
the  same  bone. 

The  naso-palatine  nerve  (nervus  naso-palatinus)  is  a  long 
slender  twig  which  can  easily  be  detected  upon  the  deep 
surface  of  the  mucous  lining  of  the  septum.  It  springs  from 
Meckel's  ganglion,  and  enters  the  nasal  fossa  through  the 
spheno- palatine  foramen.  In  the  first  part  of  its  course  it 
runs  horizontally  inwards  upon  the  under  surface  of  the  body 
of  the  sphenoid.  Having  gained  the  nasal  septum,  it  changes 
its  direction  and  proceeds  downwards  and  forwards  in  a  shallow 
groove  on  the  surface  of  the  vomer  under  cover  of  the  mucous 
lining.  Finally  it  enters  the  foramen  of  Scarpa,  and  where 
the  two  foramina  of  Scarpa  open  into  the  common  anterior 
palatine  canal,  the  nerves  of  opposite  sides  unite  in  a  plexus 


NASAL  FOSS^  391 

from  which  branches  are  given  to  the  mucous  membrane 
covering  the  fore-part  of  the  hard  palate.  The  naso-palatine 
nerve  is  accompanied  by  the  corresponding  artery,  and  as  it 
lies  on  the  surface  of  the  vomer,  it  supplies  some  small  twigs 
to  the  mucous  membrane  of  the  septum  nasi. 

A  few  nasal  branches  from  Meckel's  ganglion,  and  also 
from  the  Vidian  nerve,  reach  the  mucous  membrane  over  the 
upper  and  back  part  of  the  septum.  They  are  very  minute, 
and  it  is  questionable  if  the  dissector  will  be  able  to  discover 
any  trace  of  them. 

The  septal  branch  of  the  nasal  nerve  proper  will  be  found 
descending  over  the  fore-part  of  the  nasal  septum.  It  runs 
between  the  mucous  membrane  and  the  septal  cartilage,  and 
its  terminal  twigs  may  be  traced  as  far  as  the  vestibule. 

The  arteries  which  convey  blood  to  the  septum  nasi  are : 
(1)  the  naso-palatine,  which  accompanies  the  nerve  of  the 
same  name;  (2)  a  branch  of  the  anterior  ethmoidal  accom- 
panying the  septal  branch  of  the  nasal  nerve ;  (3)  some  minute 
twigs  to  the  upper  part  of  the  septum  from  the  posterior  eth- 
moidal artery ;  (4)  the  septal  branch  of  the  superior  coronary 
artery,  which  is  distributed  upon  the  columna  nasi. 

Dissection. — The  mucous  membrane  of  the  septum  may  now  be  divided 
by  the  scissors  along  the  roof  of  the  nasal  cavity.  Before  doing  this, 
disengage  from  its  surface  the  naso-palatine  nerve  and  the  septal  branch 
of  the  nasal  nerve  proper,  in  order  that  they  may  be  afterwards  traced  to 
their  origins.  When  the  layer  of  mucous  membrane  thus  detached  from 
the  roof  of  the  nose  is  thrown  inwards  the  nasal  fossa  is  exposed. 

Nasal  Fossse  (cavum  nasi). — These  are  two  chambers 
placed  one  on  each  side  of  the  septum  nasi.  They  are  extremely 
narrow,  but  the  vertical  depth  and  antero-posterior  length 
of  each  fossa  is  very  considerable.  The  width  increases 
somewhat  from  above  downwards ;  thus,  in  the  upper  part, 
the  superior  turbinated  bone  is  only  separated  from  the 
septum  by  an  interval  of  2  mm.,  whilst  lower  down  we  find 
a  space  of  4  or  5  mm.  intervening  between  the  inferior 
turbinated  bone  and  the  septum.  Each  nasal  fossa  presents 
an  inner  wall  formed  by  the  septum,  an  outer  wall,  a  roof,  a 
floor,  and  an  anterior  and  a  posterior  aperture. 

The  anterior  apertures  of  the  nasal  fossae  or  nostrils  are 
two  oval  orifices  which  open  upon  the  face  and  look  down- 
wards. The  posterior  apertures  or  choanal  open  into  the  naso- 
pharynx and  look  directly  backwards. 


192 


HEAD  AND  NECK 


The  narrow  roof  of  the  nasal  fossa  consists  of  an  inter- 
mediate horizontal  portion  formed  by  the  cribriform  plate  of 
the  ethmoid  bone,  and  of  an  anterior  and  a  posterior  sloping 
part.  The  anterior  part  inclines  downwards  and  forwards, 
and  is  formed  by  the  narrow  grooved  nasal  surface  of  the 
nasal  spine  of  the  frontal  bone,  the  nasal  bone,  and  the  angle 


Anterior 
ethmoidal  cell 


Infundibulum 


Posterior  angle  of 

septal  cartilage 

between  vomer. 

and  perpendicular 

plate  of  ethmoid 


■Middle  meatus 
Middle  turbin- 
ated bone 


Antrum  of 
Highmore 


Inferior  meatus 


Inferior  turbinated  bone 


Fig.  143. — Coronal  section  through  the  Nasal  Cavities  opposite  the 
Crista  Galli  of  the  Ethmoid  Bone  ;  viewed  from  behind. 

The  upper  arrow  passes  through  the  opening  of  the  anterior  ethmoidal  cell  into  the 
hiatus  semilunaris.  The  lozver  arrow  passes  from  the  antrum  of  Highmore  into  the 
hiatus  semilunaris. 


between  the  lateral  cartilage  and  the  septal  cartilage.  The 
posterior  part  of  the  roof,  which  slopes  downwards  and  back- 
wards, is  composed  of  the  fore  and  under  surfaces  of  the 
body  of  the  sphenoid,  as  well  as  the  spread-out  ala  of  the 
vomer  and  the  sphenoidal  process  of  the  palate  bone,  both 
of  which  are  applied  to  the  under  surface  of  the  sphenoidal 
body. 

The  floor  of  the  nasal  fossa  is  of  considerable  width.      It  is 


NASAL  FOSS.E  393 

formed  by  the  palatal  processes  of  the  superior  maxillary 
and  palate  bones,  and  is  concave  from  side  to  side.  Further, 
it  presents  a  gentle  slope  from  before  backwards,  being 
slightly  higher  in  front  than  behind.  On  the  anterior  part  of 
the  floor,  and  close  to  the  septum  nasi,  the  dissector  may 
observe  a  minute  funnel-shaped  depression  of  the  mucous 
membrane  into  the  incisor  foramen.  This  is  of  interest  from 
a  developmental  point  of  view  ;  it  is  a  vestige  of  the  extensive 
communication  which  existed  in  the  embryo  between  the 
cavities  of  the  nose  and  the  mouth. 

Outer  Wall  of  the  Nasal  Fossa. — The  outer  wall  of  the 
nasal  cavity  is  rendered  uneven  and  complicated  by  the  pro- 
jection of  the  three  turbinated  bones. 

The  part  which  the  different  bones  take  in  the  formation  of  the  outer 
wall  of  the  cavity  of  the  nose  must  in  the  first  place  be  studied  in  a 
sagittal  section  through  the  macerated  skull,  and  the  dissector  should 
constantly  refer  to  such  a  preparation  during  the  dissection.  In  front, 
the  outer  wall  of  the  nasal  cavity  is  formed  by  the  lateral  cartilage,  the 
cartilage  of  the  aperture,  the  nasal  bone,  and  the  ascending  process  of 
the  superior  maxillary  bone.  Behind  these,  the  lachrymal,  the  ethmoid, 
and  the  inferior  turbinated  bones,  with  a  small  portion  of  the  body  of 
the  superior  maxillary  bone,  enter  into  its  construction ;  whilst  still 
farther  back  are  the  vertical  plate  of  the  palate  bone  and  the  internal 
pterygoid  plate  of  the  sphenoid.  Placed  in  relation  to  the  outer  aspect 
of  this  wall  are  the  ethmoidal  air-cells,  which  intervene  between  the 
upper  part  of  the  nasal  cavity  and  the  orbit,  whilst,  at  a  lower  level,  the 
great  air  sinus  of  the  superior  maxillary  bone,  termed  the  antrum  of 
Ilighmore,  is  situated  immediately  to  the  outer  side  of  the  nasal  fossa 
(Fig.  143). 

Turning  now  to  the  recent  specimen,  the  dissector  will 
observe  that  the  outer  wall  may  very  readily  be  subdivided 
into  three  areas  or  districts.  These  are — (1)  the  vestibule, 
(2)  the  atrium  meatus  medii,  (3)  the  region  of  the  turbinated 
bones  and  intervening  meatuses. 

Vestibulum  Nasi. — The  vestibular  part  (Pig.  144,  6,  6') 
of  the  outer  wall  is  a  depression  of  a  somewhat  oval  form 
placed  immediately  above  the  aperture  of  the  nostril.  It  is 
partially  divided  into  an  upper  and  lower  portion  by  a  short 
ridge  which  projects  forwards  from  its  posterior  boundary, 
and  it  is  clothed  throughout  by  integument  continuous  with 
the  skin.  From  this  a  number  of  stout,  stiff  hairs,  termed 
vibrissa',  project  (Fig.  144,  5).  The  vibrissas  which  spring 
from  the  anterior  part  of  the  region  incline  backwards,  whilst 
those  which  are  implanted  into  the  posterior  part  are  directed 
forwards ;  in  this  manner  a  sieve-like  arrangement  is  provided 


394 


HEAD  AND  NECK 


at  the  anterior  aperture  of  the  nose.  The  vestibular  part  of 
the  outer  wall  is  placed  opposite  the  corresponding  area  on 
the  septum  nasi,  and  the  two  together  constitute  an  ampullated 
entrance  to  the  nasal  fossa.      The  capacity  and  shape  of  this 


Fig.  144. — Outer  Wall  of  the  Left  Nasal  Fossa.      (From  Schwalbe. ) 


1.  Frontal  air  sinus. 

2.  Free  border  of  the  nasal  bone. 

3.  Cribriform  plate  of  ethmoid. 

4.  Sphenoidal  air  sinus. 

5.  Vibrissas. 

6',  6.  Two  parts  of  the  vestibular  area. 

7.  Elevation     intervening     between     the 

vestibular  district  and  the  atrium. 

8.  Atrium  meatus  medii. 

9.  Agger  nasi,  or  rudiment  of  an  anterior 

turbinal. 

10.  Upper  part  of  the  superior  turbinated 

bone  (concha  suprema) 

11.  Recessus  spheno-ethmoidalis. 


12.  Superior  turbinated  bone. 

13.  Superior  meatus. 

14.  Middle  turbinated  bone. 

15.  Inferior  turbinated  bone. 

16.  Plica  naso-pharyngea. 

17.  District  intermediate  between  nose  and 

pharynx,  and   termed  the   region  of 
the  ductus  naso-pharyngeus. 

18.  Orifice  of  Eustachian  tube. 

19.  Prominent  posterior  lip  of  this  orifice. 

20.  Wall  of  pharynx. 

21.  Anterior  palatine  canal. 

a,  b,  c.   Free  border  of  the  middle  turbin- 
ated bone. 


section  of  the  cavity  is  influenced  to  a  certain  extent  by  the 
contraction  of  the  nasal  muscles. 

Atrium  Meatus  Medii. — This  part  of  the  outer  wall  of  the 
nasal  fossa  (Fig.  144)  is  placed  above,  and  slightly  behind 
the  vestibular  district,  and  it  receives  its  name  from  the  fact 
that  it  leads  directly  backwards  into  the  middle  meatus  of 


NASAL  FOSSAE  395 

the  nose.  It  is  slightly  hollowed  out  and  concave,  and  on 
its  upper  part,  near  the  nasal  bone,  a  feeble  elevation  termed 
the  agger  nasi  may  be  noticed ;  this  begins  close  to  the  fore- 
part of  the  attached  margin  of  the  middle  turbinated  bone, 
and  proceeds  obliquely  downwards  and  forwards.  It  has 
been  termed  by  Schwalbe  the  "  rudiment  of  the  anterior 
turbinal,"  and  he  considers  that  it  is  the  representative  of  the 
naso-turbinal  which  is  present  in  some  mammals.  A  slight 
depression  above  the  agger  nasi  leads  backwards  to  the  olfac- 
tory district  of  the  outer  wall  of  the  nasal  fossa,  and  receives 
the  name  of  sulcus  ol f actor ius. 

Turbinated  Bones. — Behind  the  vestibule  and  the  atrium 
are  the  turbinated  bones  with  the  intervening  meatuses.  The 
superior  turbinated  bone  (concha  superior)  (Fig.  144),  which 
projects  from  the  lateral  mass  of  the  ethmoid  bone,  is  very 
short,  and  is  placed  on  the  upper  and  back  part  of  the  outer 
wall  of  the  fossa.  Its  free  border  begins  a  short  distance 
below  the  centre  of  the  cribriform  plate,  and  proceeds 
obliquely  downwards  and  backwards  to  a  point  immediately 
below  the  body  of  the  sphenoid,  where  it  ends.  The  middle 
turbinated  bofie  (concha  media)  (Fig.  144)  is  also  a  part  of 
the  ethmoid.  Its  free  border  begins  a  short  distance  below 
the  fore-part  of  the  cribriform  plate,  and  at  first  takes  a  vertical 
course  downwards ;  then,  bending  suddenly,  it  proceeds 
backwards,  and  ends  midway  between  the  body  of  the 
sphenoid  and  the  posterior  border  of  the  hard  palate. 
The  inferior  turbinated  bone  (concha  inferior)  (Fig.  144)  is  an 
independent  bone,  and  stretches  backwards  upon  the  outer 
wall  of  the  nasal  fossa,  midway  between  the  middle  turbinated 
bone  and  the  floor  of  the  nose.  Its  lower  free  margin  is 
somewhat  convex  from  before  backwards. 

Meatuses  of  the  Nose  (meatus  nasi). — The  superior  meatus 
(Fig.  144)  is  a  short  narrow  fissure  between  the  superior  and 
middle  turbinated  bones.  The  posterior  ethmoidal  cells  open 
into  its  upper  and  fore  part  by  one,  or,  in  some  cases,  by 
several  apertures. 

To  bring  these  orifices  into  view,  the  superior  spongy  bone  should  be 
turned  aside  by  introducing  the  blade  of  a  pair  of  forceps  under  its  entire 
length,  and  forcing  it  upwards.  Care  should  be  taken  not  to  injure  the 
mucous  membrane  more  than  is  absolutely  necessary. 

The  middle  meatus  is  a  much  more  roomy  passage  which 


396 


-*- 


HEAD  AND  NECK 


lies  between  the  middle  and  inferior  turbinated  bones,  and  is 
continued  directly  forwards  into  the  atrium. 

The  middle  spongy  bone  should  be  forcibly  tilted  upwards  and  back- 
wards. 

The  upper  and  fore  part  of  the  middle  meatus  leads  into  a 
funnel-shaped  passage  which  passes  upwards  into  the  corre- 
sponding frontal  sinus.  This  passage  is  called  the  infundi- 
bulum,  and  constitutes  the  channel  of  communication  between 
the  frontal  sinus  and  the  nasal  chamber. 


Frontal  air-sinus 

Bulla  ethmoidalis 

Orifice  of  middle  ethmoidal  cells 

Orifices  of  posterior  ethmoidal  cells 

Recessus  spheno-ethmoidalis 
enoidal  sinus 


Orifice  of  anterior 
ethmoidal  cells 


Hiatus  semilunaris 

Atrium 

Orifice  of  antrum 
of  Highmore 


Vestibule 


Orifice  of  nasal  duct 


Cut  edge  of 
middle  turbinated 
bone 

—Middle  meatus 

Pharyngeal 
T    recess 
^      Eustachian 
:tt — orifice 

Salpingo- 

i     \  pharyngeal  fold 

>^ttt— Soft  palate 


Inferior  meatus 


Cut  edge  of  inferior 
turbinated  bone 


Fig.  145. — Outer  wall  of  Nasal  Chamber  and  Naso-pharynx.      The 
three  turbinated  bones  have  been  removed. 


Upon  the  lateral  wall  of  the  middle  meatus  a  deep  curved 
groove  or  gutter,  which  takes  origin  at  the  infundibulum  and 
runs  from  above  downwards  and  backwards,  will  be  observed. 
In  this  groove,  which  is  termed  the  hiatus  semilunaris  (Fig. 
145),  are  the  openings  of  the  anterior  ethmoidal  cells,  and 
the  antrum  of  Highmore.  The  upper  boundary  of  the  hiatus 
semilunaris  is  prominent  and  bulging.  It  is  termed  the  bulla 
ethmoidalis.  At  a  higher  level  than  the  bulla  the  aperture  of 
the  middle  ethmoidal  cells  will  usually  be  seen  (Fig.  145). 
The  slit -like  opening  of  the  antrum  of  Highmore  will  be 
noticed  in  the  hinder  part  of  the  hiatus  semilunaris. 


NASAL  FOSSAE  397 

The  dissector  should  now  proceed  to  open  up  the  antrum  of  Highmore 
by  removing  its  outer  wall.  This  may  be  done  by  sawing  upwards  through 
the  root  of  the  zygomatic  process  of  the  superior  maxillary  bone. 

The  orifice  by  means  of  which  this  great  air  sinus  com- 
municates with  the  middle  meatus  will  be  noticed  to  be 
placed  on  the  inner  wall  of  the  cavity  much  nearer  the  roof 
than  the  floor — a  position  highly  unfavourable  for  the  escape 
of  fluids  which  may  collect  within  it.  Sometimes,  however, 
a  second  orifice,  circular  in  outline,  will  be  found.  This  is 
situated  lower  down,  and  opens  into  the  middle  meatus 
immediately  above  the  middle  point  of  the  attached  margin 
of  the  inferior  turbinated  bone. 

The  inferior  meatus  is  the  horizontal  passage  which  extends 
backwards  between  the  inferior  turbinated  bone  and  the  floor 
of  the  nasal  fossa.  It  is  placed  behind  the  vestibule,  and  the 
free  border  of  the  projection,  which  corresponds  to  the  inferior 
turbinated  bone,  turns  downwards  in  front  so  as  to  limit  it 
anteriorly  (Fig.  144).  This  condition,  together  with  the  back- 
ward slope  of  the  floor,  renders  the  inferior  meatus  more 
accessible  to  the  current  of  expired  air  than  to  the  current  of 
inspired  air.  In  the  fore-part  of  this  meatus  will  be  found  the 
opening  of  the  nasal  duct — the  canal  which  conveys  the  tears 
to  the  nasal  fossa  (Fig.  145). 

To  bring  the  aperture  of  the  nasal  duct  into  view,  remove  a  small 
portion  of  the  anterior  part  of  the  inferior  turbinated  bone  with  the  scissors. 

The  orifice  of  the  nasal  duct  varies  in  form,  according  to 
the  manner  in  which  the  mucous  membrane  is  arranged 
around  it.  Sometimes  it  is  wide,  patent,  and  circular;  at 
other  times  the  mucous  membrane  is  prolonged  inwards 
beyond  the  bony  opening,  so  as  to  reduce  the  size  of  the 
aperture  and  even  give  it  a  slit-like  character.  In  some  cases 
indeed  the  orifice  may  be  so  minute  that  it  is  a  difficult 
matter  to  find  it.  Its  continuity  with  the  lachrymal  sac 
should  in  all  cases  be  established  by  passing  a  probe  from 
above  downwards  through  the  nasal  duct. 

A  fourth  meatus  is  generally  present  on  the  outer  wall  of 
the  nose.  It  is  not  at  all  uncommon  to  find  the  superior 
turbinated  bone  partially  subdivided  into  an  upper  and  lower 
part  by  a  short  groove,  which  proceeds  forwards  from  the 
anterior  aspect  of  the  body  of  the  sphenoid.  This  additional 
meatus  is  termed  the  recessus  splieno-ethmoidalis  (Meyer),  and 


398  HEAD  AND  NECK 

into  its  back-part  opens  the  aperture  of  the  sphenoidal  air 
sinus  (Fig.  145).  This  orifice  may  be  circular  or  slit-like, 
according  to  the  manner  in  which  the  mucous  membrane  is 
disposed  around  it.1  The  upper  portion  of  the  superior 
turbinated  bone  which  is  placed  above  this  additional  meatus 
is  called  the  concha  suprema  (Fig.  144). 

Mucous  Membrane  of  the  Outer  Wall  of  the  Nose. — The 
vestibule,  as  we  have  noted,  is  lined  by  integument.  The 
remainder  of  the  outer  wall,  as  well  as  the  roof  and  floor  of 
the  nasal  fossa,  is  lined  by  mucous  membrane,  which  is  con- 
tinuous through  the  nasal  duct  with  the  ocular  conjunctiva, 
through  the  various  apertures  with  the  delicate  lining 
membrane  of  the  air-cells  which  open  into  the  nose,  and 
through  the  posterior  nares  with  the  pharyngeal  mucous 
membrane.  On  the  outer  wall,  as  on  the  septum,  the 
mucous  membrane  is  mapped  out  into  an  upper  olfactory  and 
a  lower  respiratory  portion.  This  subdivision  cannot  be 
appreciated  by  the  naked  eye,  as  the  one  district  passes 
without  any  sharp  line  of  demarcation  into  the  other.  The 
olfactory  region  (regio  olfactoria)  comprises  merely  the  upper 
turbinated  bone ;  the  respiratory  region  (regio  respiratoria) 
includes  the  middle  and  inferior  turbinated  bones,  the  middle 
meatus,  the  lower  meatus,  and  the  atrium.  In  the  lower  part 
of  the  outer  wall  the  mucous  membrane  is  thick  and  spongy. 
This  is  particularly  noticeable  over  the  lower  borders  and 
posterior  extremities  of  the  middle  and  inferior  turbinated 
bones,  where  the  membrane  presents  an  irregular  surface  and 
forms  soft  bulging  cushions.  This  condition  is  largely  due  to 
the  presence  of  a  rich  venous  plexus,  the  vessels  of  which  run 
for  the  most  part  in  an  antero-posterior  direction.  In  the 
case  of  the  lower  spongy  bone,  the  veins  are  so  numerous 
that  the  mucous  membrane  assumes  the  character  of  cavernous 
tissue,  and  is  sometimes  spoken  of  as  the  "erectile  body." 
When  turgid  with  blood,  it  swells  out  so  as  to  obliterate  the 
interval  between  the  turbinal  bone  and  the  septum.  The 
mucous  membrane  of  the  floor,  meatuses,  and  the  atrium,  is 
smoother  than  and  not  so  thick  as  that  over  the  turbinated 
bones.  Everywhere  numerous  racemose  glands  are  embedded 
in  its  midst,  and  the  minute  punctiform  orifices  of  the  ducts 

1  When  the  recessus  spheno-ethmoidalis  is  absent,  the  sphenoidal  air  sinus 
opens  into  the  interval  between  the  roof  of  the  nasal  fossa  and  the  superior 
turbinated  bone. 


NASAL  FOSSAE  399 

are  visible  to  the  naked  eye.  In  the  olfactory  region  the 
lining  membrane  of  the  nose  in  the  fresh  state  is  of  a  yellowish 
colour,  and  is  softer  and  more  delicate  than  in  the  respiratory 
part. 

The  great  vascularity  of  the  mucous  membrane  of  the  nose 
is  doubtless  for  the  purpose  of  moistening  and  raising  the 
temperature  of  the  inspired  air. 

Nerves  and  Vessels  on  the  Outer  Wall  of  the  Nasal 
Fossa : — 

Nerves  of  Smell,    .     Olfactory  nerves. 

'1.    External  branch  of  nasal  proper. 

2.  Nasal  branch  of  anterior  superior  dental. 

3.  Superior  nasal   branches  from   Meckel's  ganglion 
and  from  the  Vidian  nerve. 

4.  Two    inferior     nasal     branches    from    the     great 
posterior  palatine  nerve. 


Nerves  of  Common 
Sensation,  . 


The  olfactory  nerves  are  from  twelve  to  twenty  in  number. 
They  are  fine  filaments  which  spring  from  the  under  surface 
and  the  extremity  of  the  olfactory  bulb,  and,  passing  through 
the  apertures  in  the  cribriform  plate  of  the  ethmoid  into  the 
nose,  they  separate  into  an  outer  and  an  inner  group.  To 
each  nerve  an  investment  from  the  cerebral  membranes  is 
given.  The  inner  or  septal  nerves  have  been  already  described 
(P-  39°)-  The  outer  nerves  descend  between  the  mucous 
membrane  and  the  periosteum  on  the  outer  wall  of  the  nose. 
At  first  lodged  in  shallow  grooves  or  minute  bony  canals,  they 
soon  divide  into  bunches  of  branches  which  spread  out  over 
the  upper  turbinated  bone  and  the  region  immediately  below. 
The  dissection  of  these  nerves  is  exceedingly  difficult  even  in 
the  fresh  subject,  but  in  a  well-preserved  part  they  can  gener- 
ally be  partially  displayed. 

The  superior  nasal  branches  which  come  from  the  spheno- 
palatine ganglion  and  from  the  Vidian  nerve  are  very  minute 
filaments,  but  the  dissector  should  not  be  deterred  on  this 
account  from  endeavouring  to  trace  them  to  their  distribution 
upon  the  outer  wall.  They  enter  the  nose  through  the 
spheno-palatine  foramen,  which  is  situated  at  the  back  part  of 
the  superior  meatus. 

The  best  plan  to  adopt  for  their  display  is  to  trace  the  naso-palatine 
nerve,  which  has  already  been  exposed  on  the  nasal  septum,  outwards 
across  the  roof  of  the  nose.  This  will  lead  to  the  foramen,  and  by  care- 
fully dissecting  the  mucous  membrane  in  its  neighbourhood  the  superior 
nasal  nerves  may  be  detected  entering  the  nasal  fossa. 


400  HEAD   AND   NECK 

They  are  distributed  to  the  mucous  membrane  over  the 
upper  and  middle  turbinated  bones ;  and  some  filaments  are 
prolonged  to  the  septum. 

The  inferior  nasal  nerves  are  two  in  number,  and  they  both 
arise  from  the  great  posterior  palatine  nerve. 

Carefully  raise  the  mucous  membrane  from  the  posterior  part  of  the 
outer  wall  of  the  nasal  fossa.  Make  a  vertical  incision,  through  the 
membrane  over  the  internal  pterygoid  process,  and  turn  it  cautiously  over 
from  behind  forwards. 

The  upper  of  the  two  inferior  nasal  nerves  will  be  found 
emerging  through  a  small  aperture  in  the  vertical  plate  of  the 
palate  bone,  at  a  point  between  the  posterior  extremities  of 
the  middle  and  inferior  turbinated  bones.  It  divides  into  an 
ascending  and  descending  branch.  The  former  runs  forwards 
on  the  middle  spongy  bone ;  the  latter  extends  forwards  upon 
the  inferior  spongy  bone.  The  lower  of  the  two  inferior  nasal 
nerves  appears  through  a  foramen  in  the  vertical  plate  of  the 
palate  bone  immediately  behind  the  posterior  end  of  the 
inferior  turbinated  bone,  upon  the  outer  surface  of  which  it 
proceeds  in  a  forward  direction. 

The  nasal  nerve  proper  should  be  exposed  as  it  descends 
in  the  groove  upon  the  deep  surface  of  the  nasal  bone  (p.  338). 
It  gives,  as  we  have  noted,  a  branch  inwards  to  the  septum ; 
an  external  twig  may  also  be  traced  to  the  mucous  membrane 
over  the  fore-part  of  the  outer  wall  and  to  the  fore-parts  of 
the  middle  and  inferior  turbinated  bones. 

The  main  artery  of  supply  to  the  nasal  mucous  membrane 
is  the  splwio-palatine,  a  branch  of  the  internal  maxillary.  It 
gains  entrance  to  the  nasal  fossa  through  the  spheno-palatine 
foramen  in  company  with  the  superior  nasal  and  naso-palatine 
nerves.  One  branch  of  this  vessel — the  naso-palatine — accom- 
panies the  latter  nerve,  whilst  others  are  distributed  upon  the 
outer  wall  of  the  cavity.  Several  twigs  are  also  given  by  the 
descending  or  posterior  palatine  branch  of  the  internal  maxillary 
and  the  two  ethmoidal  arteries,  but  these  are  small  and  will 
only  be  seen  in  cases  where  the  injection  of  the  subject  has 
been  unusually  successful. 


SPHENOPALATINE  GANGLION  401 


SPHENO-PALATINE  GANGLION  AND  INTERNAL 
MAXILLARY  ARTERY. 

The  spheno-palatine  ganglion  or  the  ganglion  of  Meckel  is 
situated  in  the  spheno-maxillary  fossa  on  the  outer  side  of  the 
spheno-palatine  foramen,  and  can  best  be  exposed  at  this 
stage  by  dissecting  from  the  inner  or  nasal  side. 

Dissection. — The  mucous  membrane  has  already  been  removed  from 
the  posterior  part  of  the  outer  wall  of  the  nasal  fossa,  and  the  inferior 
nasal  branches  of  the  great  palatine  nerve  have  been  found  piercing  the 
vertical  plate  of  the  palate  bone.  The  dissector  cannot  fail  to  notice  the 
course  taken  by  the  trunk  from  which  these  filaments  arise.  The  lamina 
of  bone  which  forms  the  inner  wall  of  the  posterior  palatine  canal  is  so 
thin  that  the  nerve  can  be  distinctly  seen  through  it.  By  carefully  opening 
up  this  canal  with  a  chisel,  and  following  the  great  palatine  nerve  upwards, 
the  dissector  will  be  led  to  the  ganglion  in  the  spheno-maxillary  fossa. 
The  naso-palatine  nerve  should  at  the  same  time  be  traced  to  its  origin. 
The  ganglion  is  so  hemmed  in  by  the  bony  walls  of  the  fossa  that  it  is  very 
difficult  to  display  it  thoroughly  ;  but  by  removing  the  orbital  process  of  the 
palate  bone,  and  a  portion  of  the  body  of  the  sphenoid,  with  the  bone 
forceps,  it  may  be  more  or  less  satisfactorily  exposed.  In  the  same 
restricted  space  will  be  found  the  terminal  portion  of  the  internal  maxillary 
artery,  from  which  numerous  branches  are  given  off. 

Spheno-palatine  Ganglion  (ganglion  sphenopalatinum). — 
This  is  a  small  triangular  flattened  body,  which  is  lodged  in  the 
spheno-maxillary  fossa.  It  is  embedded  in  soft  fat,  and  sur- 
rounded by  the  terminal  branches  of  the  internal  maxillary 
artery.  The  two  stout  spheno  -  palatine  branches  which 
descend  from  the  superior  maxillary  nerve  join  it  from  above, 
but  only  a  certain  proportion  of  their  fibres  are  involved  in 
the  ganglion ;  the  remainder  are  continued  directly  into  the 
nasal  and  palatine  nerves  which  proceed  from  the  ganglion. 
The  spheno-palatine  nerves  may  be  regarded  as  constituting 
the  sensory  roots  of  the  ganglion. 

From  the  spheno-palatine  ganglion  branches  are  given  off 
which  radiate  in  four  directions — viz.,  inwards  to  the  nose ; 
downwards  to  the  palate ;  backwards  to  establish  connexions 
with  the  facial  nerve  and  carotid  plexus,  as  well  as  to  supply 
the  mucous  membrane  of  the  pharynx ;  and  upwards  to  the 
orbit. 

T   .         ,  ,  .  f  Superior  nasal. 

Internal  branches,       .  WT  1  r~„ 

'  \  Naso-palatine. 

[Large  posterior  palatine. 

Descending  branches,   -|  Small  posterior  palatine. 

I  Accessory  posterior  palatine. 

VOL.  II — 26 


4o2  HEAD  AND  NECK 

Posterior  branches,     .  \  ™         '       , 
^  Pharyngeal. 

Ascending  branches,  .      Orbital. 

From  the  internal  maxillary  artery  twigs  are  given  off 
which  accompany  these  nerves. 

The  superior  nasal  and  the  naso-palatine  nerves  have  been 
already  described  (pp.  399  and  390).  They  arise  from  the 
inner  aspect  of  the  ganglion,  but  in  some  cases  the  naso- 
palatine may  be  seen  to  take  origin  from  the  commencement 
of  a  common  palatine  trunk,  or  even  from  one  of  the  spheno- 
palatine branches  of  the  superior  maxillary  nerve. 

The  posterior  palatine  nerves  (nervi  palatini)  are  three  in 
number,  and  are  distinguished  as  large,  small,  and  accessory. 
As  a  rule  these  spring  by  a  common  trunk  from  the  lower 
aspect  of  the  ganglion.  This  descends  in  the  posterior 
palatine  canal,  which  has  already  been  opened  up,  but  to 
expose  the  nerves  a  dense  fibrous  investment  must  be  re- 
moved. The  nerve-trunk  will  then  be  observed  to  break  up 
into  its  three  constituents. 

Dissection. — Trace,  in  the  first  instance,  the  two  smaller  nerves — viz., 
the  small  and  the  accessory  posterior  palatine  branches.  These  leave  the 
main  canal,  and  enter  smaller  tunnels,  which  conduct  them  through  the 
tuberosity  of  the  palate  bone.  Before  opening  these  up  it  is  well  to  secure 
the  nerves  as  they  emerge  from  the  lower  openings  of  the  canals.  This 
can  very  readily  be  done  by  dissecting  behind  the  hamular  process,  and 
gently  separating  the  soft  parts  from  the  under  aspect  of  the  tuberosity  of 
the  palate  bone.  As  the  dissection  is  being  made  from  the  inside,  the 
small  posterior  palatine  nerve  will  be  first  encountered,  and  it  will  be  seen 
to  pass  backwards  into  the  soft  palate,  under  cover  of  the  tendinous 
expansion  of  the  tensor  palati.1  This  must  be  divided,  in  order  that  the 
posterior  palatine  nerve  may  be  followed  to  its  distribution.  The  accessory 
posterior  palatine  ne)"ve  will  be  found  issuing  from  its  canal  a  short  distance 
to  the  outer  side  of  the  preceding  nerve.  It  is  distributed  to  the'soft  palate 
in  the  neighbourhood  of  the  tonsil.  It  is  smaller  than  the  posterior 
palatine  nerve,  and  is  sometimes  absent.  The  large  posterior  palatine 
nerve  should  now  be  followed  onwards  to  the  hard  palate.  To  do  this  the 
lower  part  of  the  posterior  palatine  canal  must  be  opened  up  by  removing 
a  small  portion  of  the  posterior  and  outer  part  of  the  horizontal  plate  of  the 
palate  bone. 

The  large  posterior  palatine  nerve,  as  it  emerges  from  the 
posterior  palatine  foramen,  turns  forwards,  and  divides  into 
branches,  which  lie  in  grooves  on  the  under  aspect  of  the 
hard  palate.      It   supplies   the  gum,   the   mucous  membrane, 

1  The  present  is  a  good  opportunity  to  observe  the  corrugated  or  wrinkled 
appearance  of  the  tendon  of  the  tensor  palati,  as  it  passes  under  the  hamular 
process. 


SPHENO-PALATINE  GANGLION  403 

and  giands  of  the  vault  of  the  mouth,  and  in  the  neighbour- 
hood of  the  anterior  palatine  foramen  it  effects  a  communi- 
cation with  the  naso- palatine  nerve.  During  its  passage 
through  the  posterior  palatine  canal  this  nerve  has  already 
been  observed  to  supply  two  mferior  nasal  branches  (p.  400). 

In  tracing  the  large  palatine  nerve  forwards  in  the  palate, 
the  dissector  should  note  the  numerous  glands  which  are 
placed  under  the  mucous  membrane  of  the  vault  of  the 
mouth,  and  the  manner  in  which  these  indent  the  bone.1 

Dissection. — Considerable  difficulty  will  be  experienced  in  exposing  the 
pharyngeal  and  Vidian  nerves.  They  proceed  backwards  from  the 
posterior  part  of  the  ganglion  in  canals  which  are  very  inaccessible. 

To  open  up  the  pterygo-palatine  canal  the  sphenoidal  process  of  the 
palate  bone  must  be  cautiously  removed  by  the  bone  forceps,  and  then 
the  dissector  should  proceed  to  open  up  the  Vidian  canal,  which  traverses 
the  root  of  the  pterygoid  process.  ■  As  the  bone  is  very  hard  and  brittle  at 
this  point,  the  dissection  must  be  effected  very  carefully. 

The  pharyngeal  nerve  occupies  the  pterygo-palatine  canal, 
and  is  distributed  to  the  mucous  membrane  of  the  upper  part 
of  the  pharynx. 

The  Vidian  nerve  (nervus  canalis  pterygoidei)  has  pre- 
viously been  seen  to  be  formed  by  a  junction  between  the 
great  superficial  petrosal  branch  of  the  facial  and  the  great 
deep  petrosal  branch  of  the  carotid  plexus  (p.  329).  It 
traverses  the  Vidian  canal,  and  joins  the  posterior  aspect  of 
the  ganglion,  of  which  it  may  be  considered  to  represent  both 
the  motor  and  sympathetic  root.  In  the  canal  it  is  invested  by 
a  strong  fibrous  envelope,  and  when  this  is  removed  it  may 
sometimes  be  noticed  to  break  up  into  a  fine  plexus  which 
surrounds  the  accompanying  artery.  It  has  already  been 
observed  to  give  some  fine  filaments  to  the  mucous  mem- 
brane of  the  nose. 

The  orbital  bra?iches  (rami  orbitales)  of  the  ganglion  are 
exceedingly  minute,  and  ascend  through  the  spheno- 
maxillary fissure  to  supply  the  periosteum  of  the  orbit. 

Termination  of  Internal  Maxillary  Artery. — The  internal 
maxillary  artery  breaks  up  into  its  terminal  branches  in  the 
spheno-maxillary  fossa.  These  have  already  been  traced. 
They  are — 

1  An  equally  good  method  of  tracing  the  large  posterior  palatine  nerve 
forwards  is  to  remove  the  palatal  processes  of  the  palate  and  superior 
maxillary  bones  with  the  bone  pliers,  and  then  to  display  the  nerve  and 
artery  on  the  upper  surface  of  the  mucous  membrane  and  glands. 


4o4  HEAD  AND  NECK 

i.  The  posterior  dental  (arteria  alveolaris  superior 
posterior)  (p.  286). 

2.  The  infra-orbital  (p.  386). 

3.  The  descending  palatine. 

4.  The  Vidian. 

5.  The  pterygo-palatine. 

6.  The  spheno-palatine. 

The  descending  palatine  (arteria  palatina  descendens) 
accompanies  the  large  posterior  palati?ie  nerve.  During  its 
passage  through  the  posterior  palatine  canal,  it  gives  off  twigs 
which  accompany  the  small  and  accessory  posterior  palatine 
nerves  and  the  two  inferior  nasal  branches  of  the  great  palatine 
nerve.  On  the  hard  palate  it  dispenses  branches  to  the 
gum,  mucous  membrane,  and  glands,  and  sends  a  small 
branch  upwards  through  the  incisor  foramen  to  anastomose 
with  the  naso-palatine  artery. 

The  Vidia?i  artery  (arteria  canalis  pterygoidei)  runs  back- 
wards in  the  Vidian  canal  to  supply  the  mucous  membrane 
of  the  upper  part  of  the  pharynx  and  of  the  Eustachian 
tube. 

The  pterygo-palatine  artery  traverses  the  canal  of  the  same 
name,  and  has  a  corresponding  distribution. 

The  spheno-palatine  (arteria  sphenopalatina)  enters  the 
nasal  fossa  through  the  spheno-palatine  foramen,  and  has 
already  been  followed  to  its  distribution  (p.  400). 


INTRAPETROUS  PART  OF  THE  FACIAL  NERVE 
AND  THE  AUDITORY  NERVE. 

The  facial  and  auditory  nerves,  together  with  the  pars 
intermedia,  have  already  been  traced  into  the  internal 
auditory  meatus  (p.  126).  The  dissector  should  now  open 
up  this  meatus  and  follow  the  facial  nerve  in  its  course 
through  the  petrous  portion  of  the  temporal  bone.  The 
canal  which  it  occupies  is  termed  the  aqueduct  of  Fallopius. 
This  begins  at  the  bottom  of  the  internal  auditory  meatus, 
and  opens  on  the  exterior  of  the  skull  at  the  stylo-mastoid 
foramen.  Between  these  points  it  pursues  a  complicated 
course,  and  this,  combined  with  the  density  of  the  bone, 
renders  the  dissection  very  difficult. 


INTRAPETROUS  PART  OF  FACIAL  NERVE     405 

Dissection. — Perhaps  the  easiest  method  of  opening  up  the  aqueduct  is, 
in  the  first  instance,  to  decalcify  the  bone  in  a  weak  solution  of  acid  ;  but, 
at  the  same  time,  it  should  be  understood  that,  with  a  little  care,  there  is 
nothing  to  hinder  the  dissector  carrying  out  the  dissection  on  the  hard  bone 
by  means  of  the  saw  and  the  chisel. 

Separate  the  temporal  bone  from  the  other  cranial  bones  which  still 
adhere  to  it,  and,  having  fixed  it  in  its  natural  position  (in  a  vice  if  possible), 
remove  the  squamous  portion  by  a  horizontal  saw-cut  at  the  level  of  the 
superior  border  of  the  petrous  bone.  A  second  horizontal  saw-cut  should 
then  be  made  through  the  pars  petrosa  immediately  above  the  roof  of  the 
internal  auditory  meatus.  If  this  is  successfully  carried  out,  the  vestibule, 
the  upper  part  of  the  tympanum,  and  the  mastoidal  cells  are  opened.  Upon 
the  upper  part  of  the  inner  wall  of  the  tympanum  above  the  stapes  and  the 
foramen  ovale,  a  prominent  ridge  will  be  noticed  running  from  before  back- 
wards. This  is  the  aqueduct  of  Fallopius.  Extend  the  opening  into  the 
tympanum  by  removing  the  remainder  of  its  roof,  and  then,  with  the  chisel, 
open  up  the  aqueduct  as  seen  in  this  part  of  its  course.  The  facial  nerve  is 
now  exposed  in  what  may  be  said  to  be  its  intermediate  or  tympanic  part. 
To  display  its  first  stage  within  the  bone,  open  up  the  internal  auditory 
meatus  by  removing  what  remains  of  its  roof,  and  follow  the  facial  nerve 
forwards  and  outwards  by  means  of  the  chisel.  This  will  lead  to  the 
geniculate  ganglion — the  swelling  which  marks  the  point  at  which  the  nerve 
bends  backwards  to  enter  the  tympanic  part  of  the  aqueduct.  Be  careful 
at  this  point  to  secure  the  branches  which  proceed  from  the  gangliform 
enlargement.  The  terminal  part  of  the  aqueduct  of  Fallopius  is  vertical, 
and  its  course  can  be  indicated  by  pushing  a  fine  pin  upwards  through  the 
stylo-mastoid  foramen.  To  open  it,  the  mastoid  process  must  be  removed 
by  a  coronal  (vertical-transverse)  saw-cut  on  a  plane  immediately  behind 
the  stylo-mastoid  foramen.  When  this  has  penetrated  the  bone  as  far  as 
that  foramen,  a  second  saw-cut  should  be  made  in  the  sagittal  (antero- 
posterior and  vertical)  direction,  to  meet  the  extremity  of  the  first.  The 
piece  of  bone  thus  marked  out  may  now  be  detached,  and  a  little  work  with 
the  chisel  will  display  the  facial  nerve  in  this  part  of  the  canal.  Three 
branches  are  given  off  from  it  here — viz.,  the  nerve  to  the  stapedius,  the 
chorda  tympani,  and  the  communicating  branch  or  branches  to  the  auricular 
nerve  from  the  vagus.  The  last  of  these  is  probably  destroyed  by  the  dis- 
section, but  the  other  two  can  be  brought  into  view  by  gently  raising  the 
nerve  from  the  anterior  wall  of  the  canal.  By  using  the  chisel  in  front,  and 
to  the  inner  side  of  the  geniculate  ganglion,  the  cochlea  will  be  exposed. 

Intrapetrous  Portion  of  the  Facial  Nerve. — As  the  facial 
nerve  traverses  the  petrous  bone,  it  may  be  divided  into  four 
stages,  which  differ  from  each  other  in  the  relations  they 
present  and  in  the  direction  which  they  take.      They  are  : — 

1.  A  part  within  the  internal  auditory  meatus. 

2.  A  very  short   part   which  extends  from    the    bottom  of  the  internal 

auditory  meatus  to  the  geniculate  ganglion. 

3.  A  part  which  occupies  that  portion  of  tin-  aqueduct  <>f  Fallopius  which 

runs  along  the  inner  wall  of  the  tympanum. 

4.  A   part    which    extends  vertically  downwards   to  the  stylo-mastoid 

foramen. 

First  stage. — In    the   internal   auditory  meatus,   the  facial 


406 


HEAD  AND  NECK 


nerve  runs  almost  directly  outwards  in  company  with  the 
auditory  nerve  and  the  pars  intermedia.  In  this  stage  of  its 
course  it  lies  in  relation  to  the  upper  and  fore  part  of  the 
auditory  nerve,  and  is  joined  by  the  pars  intermedia.  At 
the  bottom  of  the  auditory  meatus  it  enters  the  aqueduct 
of  Fallopius. 

Second  stage. — The  second  part  of  the  facial  nerve  is  very 
short.      It   runs  outwards   with   a  slight  inclination  forwards 

,-Portio  intermedia 
, -''.-Geniculate  ganglion 


Facial- 


Stapedius 


Large  superficial  petrosal 

,-  Small  superficial  petrosal 
-Small  deep  petrosal 

,-Large  deep  petrosal 
.Vidian 


\J^~ ^l'c  SanS'i°n 

Lingual 


j»  Superior  maxillary 
Spheno-palatine 


KIP  ganglion 


Digastric. 
Stylo-hyoid 


From  great  -- 
auricular 


From  auriculotemporal 
---Temporo-facial 

Cervico-facial 


Fig.   146. — Diagram  of  the  Facial  Nerve.      (Thane,  Quairi s  Anatomy.) 


C/i.  Ty.  Chorda  tympani ;  its  middle  part 
is  removed. 
Ty.   Tympanic  branch  of  the  glosso- 
pharyngeal. 


Sy.  Sympathetic     on      the    internal 
carotid  artery. 
Car,  Ty.  Caroticotympanic  nerve. 


between  the  vestibule  and  cochlea,  and  very  soon  ends  in 
the  swelling  termed  the  geniculate  ganglion. 

Third  stage. — At  the  geniculate  ganglion,  the  facial  nerve 
bends  suddenly  and  then  proceeds  backwards  and  slightly 
downwards  in  that  portion  of  the  aqueduct  which  runs  along 
the  upper  part  of  the  inner  wall  of  the  tympanum,  immedi- 
ately above  the  fenestra  ovalis. 

The  first  three  portions  of  the  facial  nerve  are  nearly 
horizontal,  and  pursue  a  somewhat  V-shaped  course.  The 
apex  of  the  V  is  directed  forwards,  and  corresponds  to  the 
geniculate  ganglion. 


INTRAPETROUS  PART  OF  FACIAL  NERVE     407 

The  fourth  stage  is  vertical,  and  arches  downwards  behind 
the  pyramid  to  gain  the  stylo-mastoid  foramen. 

The  branches  which  spring  from  the  facial  nerve  during  its 
passage  through  the  temporal  bone  are : — 

1.  The  great  superficial  petrosal  nerve,  "| 

2.  Communicating  twig  to  tympanic  branch  of  the  |  from  geniculate 

glosso-pharyngeal,  J        ganglion. 

3.  External  superficial  petrosal  nerve,  J 

4.  Nerve  to  stapedius. 

5.  Chorda  tympani. 

6.  Communicating  twigs  to  the  auricular  branch  of  vagus. 

The  great  superficial  petrosal  nerve  has  already  been 
examined  (p.  329).  Its  origin  from  the  geniculate  ganglion 
of  the  facial  can  now  be  established  by  breaking  through  the 
roof  of  the  hiatus  Fallopii  with  the  chisel. 

The  communicating  branch  to  the  tympanic  nerve  arises 
from  the  geniculate  ganglion,  and  its  union  with  the  tympanic 
forms  the  small  superficial  petrosal  nerve  (p.  314). 

The  external  superficial  petrosal  nerve  is  not  always  present. 
It  joins  the  sympathetic  plexus  which  accompanies  the  middle 
meningeal  artery. 

The  nerve  to  the  stapedius  muscle  arises  from  the  facial  as 
it  arches  downwards  behind  the  pyramid.  It  enters  the  base 
of  the  pyramid  and  thus  reaches  the  stapedius  muscle. 

The  communicating  twigs  to  the  auricular  branch  of  the 
vagus  arise  a  short  distance  above  the  stylo-mastoid  foramen. 

Chorda  Tympani. — The  chorda  tympani,  which  represents 
the  pars  intermedia  set  free  from  the  facial  nerve,  is  the 
largest  branch  which  is  given  off  by  the  facial  during  its 
passage  through  the  aqueduct  of  Fallopius.  It  takes  origin 
a  short  distance  above  the  stylo-mastoid  foramen,  and  arching 
upwards  and  forwards  in  a  narrow  canal  in  the  petrous  portion 
of  the  temporal  bone  (iter  chordae  posterius)  it  appears  in  the 
tympanum  below  the  base  of  the  pyramid,  and  close  to  the 
posterior  margin  of  membrana  tympani.  The  bony  tunnel 
which  it  occupies  can  easily  be  opened  up  in  a  decalcified 
bone,  but  is  somewhat  difficult  to  expose  in  the  hard  bone. 
The  chorda  tympani  now  runs  forwards  upon  the  upper 
part  of  the  membrana  tympani  under  cover  of  the  mucous 
layer.  It  crosses  the  handle  of  the  malleus  near  its  root. 
To  display  it  in  this  part  of  its  course,  the  incus  bone 
should  be  removed.  Finally,  reaching  the  anterior  end  of 
the  tympanic  cavity  it  crosses  the  processus  gracilis  of  the 


4o8  HEAD  AND  NECK 

malleus,  and  near  the  inner  end  of  the  Glaserian  fissure  it 
enters  a  canal  (canal  of  Huguier)  which  conducts  it  to  the 
exterior  of  the  skull.  With  a  little  care  the  canal  of  Huguier 
can  be  opened  up  by  the  chisel  and  bone  pliers.  From  this 
point  to  its  junction  with  the  lingual  nerve  the  chorda  tympani 
has  already  been  traced  (p.  294). 

Auditory  Nerve. — In  the  internal  auditory  meatus  the 
auditory  nerve  lies  at  a  lower  level  than  the  facial,  and  at  the 
bottom  of  the  passage  it  splits  into  two  parts,  termed  the 
cochlear  and  vestibular  divisions.  These  trunks  again  sub- 
divide and  supply  the  different  parts  of  the  labyrinth  of  the 
ear  through  the  foramina  of  the  lamina  cribrosa. 


THE  LARYNX. 

The  lateral  portions  of  the  lower  jaw  which  are  still 
attached  by  mucous  membrane  to  the  sides  of  the  tongue 
should  be  removed,  and  the  dissection  of  the  larynx  com- 
menced. 

General  Construction  and  Position. — The  larynx  con- 
stitutes the  upper  expanded  portion  of  the  air-passage, 
specially  modified  for  the  production  of  the  voice.  Its  walls 
are  composed  of  cartilages,  muscles,  ligaments,  and  an  in- 
ternal lining  of  mucous  membrane.  Before  proceeding  with 
the  dissection  the  student  should  study  the  form  and  con- 
nexions of  the  nine  laryngeal  cartilages  in  a  permanent  speci- 
men (v.  p.  425). 

The  larynx  is  placed  in  the  upper  and  fore  part  of  the 
neck,  where  it  forms  a  marked  projection.  It  lies  below 
the  hyoid  bone  and  tongue,  whilst  inferiorly  it  is  directly 
continuous  with  the  trachea.  In  front  it  is  covered  by  the 
integument  and  deep  cervical  fascia,  and  on  either  side  of  the 
mesial  plane  by  two  thin  strata  of  muscles,  viz.,  the  sterno- 
hyoid, the  omo-hyoid,  the  sterno-thyroid,  and  the  thyro-hyoid. 
As  a  general  rule  a  narrow  process  of  the  thyroid  body,  termed 
the  central  lode,  is  also  continued  upwards  on  its  anterior 
surface.  On  each  side  the  lateral  lobe  of  the  thyroid  body  is 
prolonged  upwards  upon  it,  and  it  is  related  to  the  great 
vessels  of  the  neck.     Posteriorly  it  is  in  relation  to  the  pharynx  • 


THE  LARYNX  409 

by  this  it  is  separated  from  the  prevertebral  muscles.  If  we 
consider  the  tip  of  the  epiglottis  to  represent  its  upper  limit, 
the  larynx  in  the  adult  may  be  regarded  as  being  placed  in 
front  of  that  portion  of  the  vertebral  column  which  extends 
from  the  lower  border  of  the  third  to  the  lower  border  of  the 
sixth  cervical  vertebra ;  but  its  position  alters  somewhat  with 
the  movements  of  the  head  and  also  during  deglutition. 

Interior  of  the  Larynx. — The  cavity  of  the  larynx  is 
smaller  than  might  be  expected  from  an  inspection  of  its 
exterior.  On  looking  into  its  interior  from  above  it  will  be 
seen  to  be  subdivided  into  three  portions  by  two  elevated 
folds  of  mucous  membrane  which  extend  from  before  back- 
wards, and  project  inwards  from  each  side  of  the  cavity.  The 
upper  pair  of  folds  are  termed  the  false  vocal  cords ;  the 
lower  pair  receive  the  name  of  the  true  vocal  cords.  The 
latter  are  the  chief  agents  in  the  production  of  the  voice,  and 
the  larynx  is  so  constructed  that  changes  in  their  relative 
position  and  in  their  degree  of  tension  are  brought  about 
by  the  action  of  the  muscles  and  the  recoil  of  the  elastic 
ligaments. 

The  Upper  Subdivision  of  the  laryngeal  cavity  (Fig.  147) 
extends  from  the  superior  aperture  of  the  larynx  down  to  the 
upper  or  false  vocal  cords.  It  is  called  the  vestibule  (vestibulum 
laryngis).  In  its  lower  part  it  exhibits  a  marked  lateral  compres- 
sion. Its  width  therefore  diminishes  from  above  downwards, 
whilst  owing  to  the  obliquity  of  the  upper  opening  of  the  larynx 
its  depth  becomes  rapidly  reduced  from  before  backwards.  In 
front  it  is  bounded  by  the  posterior  surface  of  the  epiglottis 
and  the  thyro-epiglottidean  ligament,  both  covered  by  mucous 
membrane.  This  wall  descends  obliquely  from  above  down- 
wards and  forwards,  and  becomes  narrower  as  it  approaches 
the  anterior  ends  of  the  false  vocal  cords.  The  lateral  wall  of 
the  vestibule  is  formed  by  the  inner  surface  of  the  aryteno- 
epiglottidean  fold.  For  the  most  part  it  is  smooth  and 
slightly  concave,  but  in  its  posterior  part  the  mucous  mem- 
brane bulges  out  in  the  form  of  two  elongated  vertical  eleva- 
tions placed  one  behind  the  other.  The  anterior  elevation  is 
formed  by  the  cuneiform  cartilage  and  a  mass  of  glands 
associated  with  it  enclosed  within  the  aryteno-epiglottidean 
fold ;  the  hinder  elevation  is  produced  by  the  anterior  margin 
of  the  arytenoid  cartilage  and  the  cartilage  of  Santorini.  A 
shallow  groove  descends   between   these   rounded  elevations 


4io 


HEAD  AND  NECK 


Epiglottis 


and  terminates  below  by  running  into  the  interval  between 
the  false  and  the  true  vocal  cords.  The  posterior  wall  of  the 
vestibule  is  narrow,  and  corresponds  to  the  interval  between 
the  upper  parts  of  the  two  arytenoid  cartilages. 

The  superior  aperture  of  the  larynx  has  already  been  ex- 
amined in  the  dissection  of  the  pharynx  (p.  376).  The  parts 
which  bound  it  should  again  be  carefully  studied. 

The   epiglottis  projects    upwards  behind    the   root  of  the 

tongue.  Its  lingual 
or  anterior  surface 
is  only  free  in  the 
upper  part  of  its 
extent,  and  is  at- 
tached to  the  back 
part  of  the  tongue 
by  a  prominent 
mesial  fold  of 
mucous  membrane, 
termed  the  glosso- 
epiglottidean  fold  or 
frenum  of  the  epi- 
glottis. Two  lateral 
folds  are  also 
present  which  con- 
nect its  margins 
with  the  lateral 
walls  of  the  phar- 
ynx •  these  are 
called     the    phar- 


Hyoid  bone 


Aryteno- 
epiglottidean  fold 


Cushion  of  epiglottis 

Thyroid  cartilage 

False  vocal  cord 
Laryngeal  sinus 

True  vocal  cord 

Thyro-arytenoid 
muscle 

Cricoid  cartilajre 


Fig. 


147. — Coronal  section  through  Larynx 
to  show  Compartments. 


yngo 
folds. 
two 


epiglotiidean 


Between  the 
layers  of 
mucous  membrane 
which  constitute 
each  of  these  three  folds,  there  is  a  small  amount  of  elastic 
tissue.  The  depression  on  each  side  between  the  tongue  and  the 
epiglottis  which  is  bounded  by  the  glosso-epiglottidean  and  the 
pharyngo-epiglottidean  folds  is  termed  the  vallecula  (Fig.  148). 
The  posterior  free  surface  of  the  epiglottis  forms,  as  we  have 
noted,  the  greater  part  of  the  anterior  boundary  of  the  vestibule 
of  the  larynx.  The  upper  part  of  this  surface  is  convex,  owing 
to  the  manner  in  which  the  upper  margin  is  curved  forwards 


THE  LARYNX 


411 


towards  the  tongue ;  below  this  there  is  a  slight  concavity 
and  still  lower  a  marked  bulging  or  convexity  over  the  upper 
part  of  the  thyro-epiglottidean  ligament.  This  swelling  is 
called  the  tubercle  or  cushion  of  the  epiglottis,  and  it  forms  a 
conspicuous  object  in  laryngoscopic  examinations  of  the 
larynx. 

The  aryteno-epiglottidean  folds  of  mucous  membrane  enclose 
between  their  two  layers  some  connective  tissue,  the  aryteno- 
epiglottidean  muscles,  and  posteriorly  the  cuneiform  cartilages, 
and  the  cornicula  laryngis  which  surmount  the  arytenoid 
cartilages.  As  already  mentioned,  these  small  nodules  of 
cartilage  raise  the  hinder  part  of  the  aryteno-epiglottidean 
fold  in  the  form 

Of  tWO    rOUnded  Base  of  tongue 


eminences  or 
tubercles  well 
seen  when  the 
larynx  is  ex- 
amined by 
means  of  the 
laryngoscope. 

The  Middle 
Subdivision  of 
the  laryngeal 
cavity  (Fig.  147) 
is  the  smallest 
of   the   three. 


Frenum 
epiglottidis 

Epiglottis 

Cushion 


True  vocal 
cord 


Cuneiform 


Cornicula  laryngis 


Fig.   148. — The  Larynx  as  seen  in  the  living  person  by 
means  of  the  laryngoscope. 


Above  it  is  bounded  by  the  false  vocal  cords,  below  by  the 
true  vocal  cords,  whilst  it  communicates  by  the  intervals 
between  these  folds  with  the  vestibule  on  the  one  hand,  and 
the  inferior  compartment  of  the  larynx  on  the  other. 

The  false  vocal  cords  (plica?  ventriculares)  are  two  pro- 
minent mucous  folds  which  extend  from  before  backwards  on 
the  side  walls  of  the  laryngeal  cavity.  They  are  soft  and 
somewhat  flaccid,  and  present  a  free  border  which  is  slightly 
arched — the  concavity  looking  downwards.  Within  the  fold  of 
mucous  membrane  which  forms  this  cord  are  contained — ( 1 )  the 
feeble  superior  thyro-arytenoid  ligament;  (2)  numerous  glands 
which  are  chiefly  aggregated  in  its  middle  part;  and  (3) 
a  few  muscle  fibres.  The  interval  between  the  false 
vocal  cords  is  sometimes  termed  the  false  glottis,  and  is  con- 
siderably   wider    than    that    between    the    true    vocal    cords. 


412 


HEAD  AND  NECK 


It  follows  from  this,  that  when  the  cavity  of  the  larynx  is 
examined  from  above,  the  four  cords  are  distinctively  visible, 
but  when  examined  from  below  the  true  cords  alone  can 
be  seen. 

The  true  vocal  cords  (plicae  vocales),  placed  below  the  false 
cords,  extend  from  the  angle  between  the  alse  of  the  thyroid 
cartilage  in  front  to  the  vocal  processes  of  the  arytenoid 
i      tt  cartilages       behind 


/Hyoid  bone 


piglottidean  ligament 

Cartilage  of  epiglottis 
Fatty  pad 
Thyro-hyoid  membrane 

Thyroid  cartilage 

Elevation  produced  by 
cuneiform  cartilage 

_,  False  vocal  cord 

Philtrum  ventriculi 
Elevation  produced 
byarytenoid  cartilag 
Laryngeal  sinus 

True  vocal  cord 
Arytenoid  muscle 

Processus  vocalis 

Cricoid  cartilage 
Cricoid  cartilage 


FlG.  149. — Mesial  section  through  Larynx  to 
show  the  Outer  Wall  of  the  Right  Half. 


The  true  vocal  cord 
is  sharp  and  pro- 
minent, and  the 
mucous  membrane 
which  is  stretched 
over  it  is  thin  and 
firmly  bound  down 
to  the  subjacent  liga- 
ment. In  colour  it 
is  pale,  almost  pearly 
white,  whilst  pos- 
teriorly the  point  of 
the  processus  vocalis 
of  the  arytenoid 
cartilage,  which 
stands  out  in  relief, 
presents  a  yellowish 
tinge.  In  section 
each  true  vocal  cord 
is  somewhat  pris- 
matic in  form,  and 
the  free  border  looks 
upwards  and  in- 
wards. 

The     true    vocal 


cords  are  the  agents  by  means  of  which  the  voice  is  produced. 
The  false  vocal  cords  are  of  little  importance  in  this  respect ; 
indeed,  they  can  in  great  part  be  destroyed,  and  no  appreci- 
able difference  in  the  voice  result. 

The  ritna  glottidis  or  glottis  vera  is  the  elongated  fissure  by 
means  of  which  the  middle  compartment  of  the  larynx  com- 
municates with  the  lower  subdivision.  It  is  placed  somewhat 
below  the  middle  of  the  laryngeal  cavity,  of  which  it  con- 
stitutes the  narrowest  part.      In  front  it  corresponds  to  the 


THE  LARYNX  413 

interval  between  the  true  vocal  cords ;  behind  it  corresponds 
to  the  interval  between  the  bases  and  vocal  processes  of  the 
arytenoid  cartilages  (Fig.  150).  It  is  composed,  therefore, 
of  two  very  distinct  parts — (1)  a  narrow  anterior  portion, 
between  the  true  vocal  cords,  involving  less  than  two -thirds 
of  its  length,  and  called  the  glottis  vocalis  (pars  intermem- 
branacea);  (2)  a  broader,  shorter  portion  between  the  arytenoid 
cartilages,  and  termed  the  glottis  respiratoria  (pars  inter- 
cartilaginea).       The    form    of    the    rima    glottidis    undergoes 


Thyroid  cartilage 


Inferior  thyro- 
arytenoid ligament 


Rima 


Vocal  process  of 
arytenoid  cartilage 

Arytenoid 

cartilage 


Fig.  150. — Diagram  of  Rima  Glottidis. 
A.  During  ordinary  easy  hreathing.  B.  Widely  open. 

frequent  alterations  during  life,  but  during  ordinary  quiet 
respiration  it  is  lanceolate  in  outline.  The  glottis  vocalis 
presents,  under  these  conditions,  the  form  of  an  elongated 
triangle  with  the  base  directed  backwards.  When  the 
glottis  is  widely  opened  the  broadest  part  of  the  fissure  is 
at  the  extremities  of  the  vocal  processes  of  the  arytenoid 
cartilages,  and  here  the  side  of  the  rima  presents  a  marked 
angle.  The  two  vocal  cords,  on  the  other  hand,  may  be 
approximated  so  closely  to  each  other,  as  in  singing  a  high 
note,  that  the  glottis  vocalis  is  reduced  to  a  linear  chink. 
The    length  of  the  entire  fissure   differs  considerably  in  the 


4i4  HEAD   AND   NECK 

two  sexes.      In  the  male  its  average  length  is  23  mm.;  in  the 
female,  17  mm. 

The  side  wall  of  the  larynx  in  the  interval  between  the 
true  and  the  false  vocal  cords  shows  a  pocket-like  depression 
or  recess,  termed  the  laryngeal  sinus  (ventriculus  laryngis). 
The  dissector  should  endeavour  to  gauge  the  extent  of  this, 
by  means  of  a  probe  bent  at  the  extremity.  The  recess 
passes  upwards,  so  as  to  undermine  somewhat  the  false  vocal 
cord,  and  its  mouth  or  orifice  is  narrower  than  its  cavity. 
Under  cover  of  the  fore-part  of  the  false  vocal  cord,  a  slit- 
like aperture  will  be  detected.  This  leads  into  the  laryngeal 
saccule  (appendix  ventriculi),  a  small  mucous  diverticulum, 
which  ascends  between  the  false  vocal  cord  and  the  ala  of  the 
thyroid  cartilage.  This  sac  is  of  variable  extent,  but  as  a  rule 
it  ends  blindly  at  the  level  of  the  upper  border  of  the  thyroid 
cartilage. 

Distend  the  sinus,  and  if  possible  the  saccule,   with  cotton  wadding. 
This  will  greatly  facilitate  the  subsequent  dissection. 

The  Lower  Subdivision  of  the  Laryngeal  Cavity  (Fig.  147) 
leads  directly  downwards  into  the  trachea.  Above,  it  is 
narrow  and  laterally  compressed,  but  it  gradually  widens  out 
until  in  its  lowest  part  it  is  circular.  It  is  bounded  by  the 
sloping  inner  surfaces  of  the  crico-thyroid  membrane,  and  by 
the  inner  aspect  of  the  cricoid  cartilage.  It  is  through  the 
anterior  wall  of  this  compartment  that  the  opening  is  made  in 
the  operation  of  laryngotomy. 

Mucous  Membrane  of  the  Larynx. — This  is  continuous 
above  with  that  lining  the  pharynx,  and  below  with  the 
mucous  lining  of  the  trachea.  Over  the  laryngeal  or  hinder 
surface  of  the  epiglottis  it  is  closely  adherent,  but  elsewhere 
above  the  level  of  the  true  vocal  cords  it  is  loosely  attached 
by  submucous  tissue.  As  it  passes  over  the  true  vocal  cords 
it  is  very  thin  and  tightly  bound  down.  In  inflammatory 
conditions  of  the  larynx  attended  by  oedema  this  prevents  the 
infiltration  of  the  submucous  tissue  extending  downwards 
below  the  rima  glottidis. 

The  mucous  membrane  of  the  larynx  has  a  plentiful  supply 
of  racemose  glands  which  secrete  mucus.  Over  the  surface 
of  the  true  vocal  cords  these  are  completely  absent. 

Dissection. — Place  the  larynx  upon  a  block  so  that  its  anterior  surface 
looks  upwards,  and  fix  it  in  this  position  with  pins.     The  branches  which 


THE  LARYNX  415 

the  external  laryngeal  nerve  gives  to  the  cricothyroid  muscle  should  in  the 
first  place  be  followed  out,  and  carefully  preserving  the  superior  and  inferior 
laryngeal  vessels  and  the  internal  and  recurrent  laryngeal  nerves,  the  dis- 
sector should  in  the  next  place  proceed  to  remove  the  thyroid  body,  and 
the  omo-hyoid,  sterno-hyoid,  sterno- thyroid,  and  thyro-hyoid  muscles. 
The  fibres  of  origin  of  the  inferior  constrictor  muscle  should  likewise  be 
cleared  away  from  the  thyroid  and  cricoid  cartilages.  The  broad  thyro- 
hyoid membrane,  the  central  portion  of  the  crico-thyroid  membrane,  and 
the  crico-thyroid  muscles  are  now  exposed,  and  their  attachments  may  be 
defined. 

Thyrohyoid  Membrane. — This  is  a  broad  membranous 
sheet,  which  occupies  the  interval  between  the  hyoid  bone 
and  the  thyroid  cartilage.  It  is  not  equally  strong  throughout, 
but  shows  a  central  thick  portion  and  a  cord-like  right  and 
left  margin,  whilst  in  the  intervals  between  these  it  is  thin 
and  weak.  The  central  thickened  part  {ligamentum  thyreo- 
hyoideum  medium)  is  largely  composed  of  elastic  fibres.  Above, 
it  is  attached  to  the  posterior  aspect  of  the  upper  margin  of 
the  body  of  the  hyoid  bone ;  whilst  below,  it  is  fixed  to  the 
sides  of  the  deep  median  notch,  which  interrupts  the  superior 
border  of  the  thyroid  cartilage.  The  upper  part  of  its  anterior 
surface  is  therefore  placed  behind  the  posterior  hollowed-out 
surface  of  the  body  of  the  hyoid  bone ;  a  synovial  bursa  is 
interposed  between  them,  and  in  certain  movements  of  the 
head  and  larynx  the  upper  border  of  the  thyroid  cartilage  is 
allowed  to  slip  upwards  behind  the  hyoid  bone.  On  each 
side  of  the  strong  central  part  the  thyro-hyoid  membrane  is 
thin  and  loose.  It  is  attached  below  to  the  upper  margin  of 
the  ala  of  the  thyroid  cartilage,  and  above  to  the  deep  aspect 
of  the  great  cornu  of  the  hyoid  bone.  It  is  pierced  by  the 
internal  laryngeal  nerve  and  superior  laryngeal  vessels.  The 
posterior  border  of  the  membrane  on  each  side  is  thickened, 
rounded,  and  cord-like  {ligamentum  thyreo-hyoideum  /atera/e), 
and  is  chiefly  composed  of  elastic  fibres.  It  extends  from  the 
tip  of  the  great  cornu  of  the  hyoid  bone  to  the  extremity  of 
superior  cornu  of  the  thyroid  cartilage.  In  this  ligament  there 
is  usually  developed  a  small  oval  cartilaginous  or  bony  nodule, 
which  is  termed  the  cartilago  t?-iticea. 

Crico-thyroid  Muscle. — The  crico-thyroid  muscle  is  placed 
on  the  side  of  the  cricoid  cartilage,  and  bridges  over  the 
lateral  portion  of  the  crico-thyroid  interval.  Taking  origin 
from  the  lower  border  and  outer  surface  of  the  anterior  arch 
of  the  cricoid  cartilage,  its  fibres  spread  out  in  an  upward  and 
backward  direction,  and  are  inserted  into  the  inner  aspect  of 


416 


HEAD  AND  NECK 


Cricothyroid  membrane 


the  lower  margin  of  the  thyroid  cartilage,  and  also  into  the 
anterior  border  of  its  inferior  cornu.  As  a  general  rule,  it  is 
divided  into  two  parts.  The  anterior  or  oblique  part  is  com- 
posed of  those  fibres  which  are  attached  to  the  ala  of  the 
thyroid  cartilage  ;  the  posterior  or  horizo?ital  part  is  formed  of 
those  fibres  which  are  inserted  into  the  inferior  cornu  of  the 
thyroid  cartilage.  It  is  closely  associated  with  the  inferioi 
constrictor  muscle.  The  crico-thyroid  muscle  is  supplied  by 
the  external  laryngeal  branch  of  the  superior  laryngeal  nerve. 
Middle  Portion  of  the  Crico-thyroid  Membrane. — This  can 

be  studied  in  the  in- 
terval between  the  two 
crico-thyroid  muscles.  It 
is  a  tense,  elastic,  and 
strong  membrane,  which 
is  attached  below  to  the 
median  part  of  the  upper 
border  of  the  anterior 
arch  of  the  cricoid  carti- 
lage, and  above  to  the 
lower  margin  of  the 
middle  portion  of  the 
thyroid  cartilage.  It  is 
pierced  by  minute  aper- 
tures, and  is  crossed 
superficially  by  the  crico- 
thyroid branch  of  the 
superior  thyroid  artery. 
On  each  side,  under  cover 
of  the  crico-thyroid  muscle,  the  lateral  part  of  the  crico-thyroid 
membrane  presents  very  different  connexions.  It  is  not 
attached  to  the  lower  border  of  the  thyroid  cartilage,  but 
stretches  upwards  into  the  interior  of  the  larynx,  and  takes 
part  in  the  formation  of  the  true  vocal  cord.  At  a  later  stage 
of  the  dissection  it  will  be  fully  exposed. 

Dissection. — The  position  of  the  larynx  must  now  be  reversed.  Fix 
it  upon  the  block  in  such  a  manner  that  its  posterior  aspect  is  directed 
upwards.  The  oesophagus  should  then  be  slit  open  by  a  mesial  incision 
through  its  posterior  wall.  Next  remove  with  great  care  the  mucous 
membrane  which  covers  the  posterior  aspect  of  the  cricoid  and  arytenoid 
cartilages.  In  doing  this,  bear  in  mind  that  the  inferior  laryngeal  artery, 
and  the  recurrent  laryngeal  nerve,  pass  upwards  between  the  thyroid  and 
cricoid  cartilages,  and  must  be  preserved. 

Upon  the  posterior  aspect  of  the  broad  lamina  of  the  cricoid  cartilage 


Oblique 
part 


Horizontal 
part 


Fig.  151. 


1  :^<i 

-The  Crico-thyroid  Muscle. 


THE  LARYNX 


4i7 


the  dissector  will  now  note  the  two  posterior  crico-arytenoid  muscles,  and 
the  attachment  of  the  tendinous  band  through  which  the  longitudinal  fibres 
of  the  oesophagus  are  fixed  to  the  cricoid  cartilage.  This  takes  origin  from 
the  prominent  mesial  ridge  on  the  back  aspect  of  the  cricoid  cartilage. 
On  the  posterior  surface  of  the  arytenoid  cartilages,  and  bridging  across 
the  interval  between  them,  the  dissector  will  observe  the  arytenoid  muscle. 
Especial  care  must  be  taken  in  cleaning  this  muscle  in  order  that  the  con- 
nexions of  the  superficial  decussating  fibres  may  be  fully  ascertained. 

The  outer  layer  of  the  right  aryteno-epiglottidean  fold  of  mucous  mem- 
brane should  now  be  cautiously  removed.     This  will  expose  the  aryteno- 
epiglottidean  muscle,  the  cuneiform  cartilage,  and  the  cartilage  of  Santorini 
of    that    side.     This    is 
perhaps  the  most  difficult 
part    of    the   dissection, 
because  the  dissector  has 
to  establish  the  continuity 
of  the  sparse  fibres  which 
compose    the   pale    ary- 
teno-epiglottidean mus- 
cle with  the  decussating 
fibres   of   the   arytenoid 
muscle. 


Epiglottis 


Aryteno-epi- 

dottidean  fold 


Cartilage  of  Santorini 

Arytenoideus 

obliquus 

Arytenoideus 

transversus 

Muscular  process 
of  arytenoid 


Crico-arytenoideus 

posticus 

Facet  for  inferior  cornu 
of  thyroid  cartilage 

Crico-arytenoideus 
posticus 


Fig. 


Posterior  Crico  - 
arytenoid  Muscle. — 
The  posterior  crico- 
arytenoid muscle  is 
somewhat  fan- 
shaped  (Fig.  152). 
It  springs  by  a  broad 
origin  from  the  de- 
pression which  marks 
the  posterior  surface 
of  the  cricoid  carti- 
lage on  each  side  of 
the  mesial  ridge,  and 
its  fibres  converge 
to  be  inserted  into  the  posterior  surface  and  outer  angle  of 
the  processus  muscularis  or  projecting  outer  angle  of  the 
base  of  the  arytenoid  cartilage.  In  pursuing  this  upward  and 
outward  course,  the  fibres  run  with  different  degrees  of 
obliquity.  The  uppermost  fibres  are  short  and  nearly 
horizontal  ;  the  intermediate  fibres  are  the  longest,  and  are- 
very  oblique ;  whilst  the  lowest  fibres  are  almost  vertical 
in  their  direction. 

Arytenoid  Muscle. — The  arytenoid  muscle  consists  of  two 
portions, — a  superficial  part,  termed  the  arytenoideus  obliquus, 
and  a  deeper  layer,  called  the  arytenoideus  transversus. 

vol.  11 — 27 


152. — Muscles  on  the  Posterior  Aspect 
of  the  Larynx. 


4iS  HEAD  AND  NECK 

The  arytenoideus  obliquus  is  composed  of  two  bundles  of 
muscular  fibres,  each  of  which  springs  from  the  posterior  aspect 
of  the  outer  angle  of  the  base  or  processus  muscularis  of  the 
corresponding  arytenoid  cartilage  (Fig.  152).  From  these 
points  the  two  fleshy  slips  proceed  upwards  and  inwards,  and 
cross  each  other  in  the  mesial  plane  like  the  limbs  of  the  letter 
X.  Reaching  the  summit  of  the  arytenoid  cartilage  on  each 
side,  some  of  the  fibres  are  inserted  into  it,  but  the  greater 
proportion  are  prolonged  round  the  base  of  the  cartilage 
of  Santorini  into  the  aryteno-epiglottidean  fold.  Here 
they  receive  the  name  of  the  aiyteno-epiglottidean  muscle, 
and  as  they  approach  the  epiglottis  they  are  joined  by  the 
fibres  of  the  thyro-epiglottidean  muscle.  The  oblique  arytenoid 
muscles  may  therefore  be  considered  as  constituting  a  weak 
sphincter  muscle  for  the  superior  aperture  of  the  larynx. 
Each  bundle  starting  from  the  base  of  one  of  the  arytenoid 
cartilages  is  prolonged  into  the  aryteno-epiglottidean  fold  of  the 
opposite  side,  and  along  this  to  the  margin  of  the  epiglottis. 

The  arytenoideus  transversus  is  an  unpaired  muscle.  It  is 
composed  of  transverse  fibres  which  bridge  across  the  interval 
between  the  two  arytenoid  cartilages,  and  are  attached  to 
the  posterior  aspect  of  the  outer  border  of  the  arytenoid 
cartilage.  Many  of  the  fibres  turn  round  the  arytenoid 
cartilage  and  become  continuous  on  each  side  with  the  fibres 
of  the  thyro-arytenoid  muscle. 

Dissection. — The  further  dissection  of  the  laryngeal  muscles  should  be 
confined  to  the  right  side  of  the  larynx.  The  left  side  should  be  reserved 
for  the  study  of  the  nerves  and  vessels.  Place  the  larynx  on  its  left  side, 
and,  having  fixed  it  in  this  position,  remove  the  right  crico-thyroid  muscle. 
The  right  lateral  thyro-hyoid  ligament  should  next  be  divided,  and  the 
right  inferior  cornu  of  the  thyroid  cartilage  disarticulated  from  its  facet  on 
the  side  of  the  cricoid  cartilage.  An  incision  should  now  be  made  through 
the  right  ala  of  the  thyroid  cartilage  a  short  distance  to  the  outer  side  of 
the  mesial  plane,  and  the  detached  piece  carefully  removed.  Three 
muscles  are  now  exposed,  and  must  be  carefully  cleaned  and  defined. 
They  are  named  from  below  upwards  : — 

1.  The  lateral  crico-arytenoid. 

2.  The  thyro-arytenoid. 

3.  The  thyro-epiglottidean. 

Lateral  Crico  -  arytenoid  Muscle.  —  The  lateral  crico- 
arytenoid muscle  is  triangular  in  form,  and  smaller  than  the 
crico-arytenoideus  posticus  (Fig.  153).  It  springs  from  the 
upper  border  of  the  lateral  part  of  the  cricoid  cartilage  as  far 
back  as  the  facet  which  supports  the  base  of  the  arytenoid 


THE  LARYNX 


419 


Epiglottic 


cartilage ;  a  few  of  its  fibres  likewise  take  origin  from  the 
crico-thyroid  membrane.  From  this  attachment  its  fibres 
run  backwards  and  upwards,  and  converge  to  be  inserted 
into  the  anterior  surface  of  the  processus  muscularis  or  outer 
projecting  angle  of  the  base  of  the  arytenoid  cartilage.  The 
superficial  or  outer  surface  of  this  muscle  is  covered  by  the 
ala  of  the  thyroid  cartilage  and  the  upper  part  of  the  crico- 
thyroid muscle ;  its  deep  surface  is  applied  to  the  lateral  part 
of  the  crico-thy- 
roid membrane. 

Thyro  -  aryte- 
noid Muscle. — 
This  is  a  muscu- 
lar sheet  which  is 
placed  above  the 
crico  -  arytenoid - 
eus  lateralis  (Fig. 
153).  The  con- 
tiguous margins 
of  these  muscles 
are  sometimes 
found  so  inti- 
mately blended 
that  it  is  impos- 
sible to  effect  a 
natural  separa- 
tion. 

The  thyroary- 
tenoid muscle  is 
usually  described 
as  consisting  of  a 
superficial  and  a 


Aryteno-epiglottidean  muscle 


oid  bone 
Cuneiform  cartilage 

Thyro-epi- 
glottidean  muscle 
Thyro-hyoid 
membrane 

Saccule  of  larynx- 
Muscular  process  of 
arytenoid  cartilage 

Thyro-arytenoid 

muscle 

Thyroid  cartilage 

Crico-arytenoideus 
lateralis 


Crico-arytenoideus 
posticus 

Crico-thyroid 
membrane 

Cricoid  cartilage 


! 

•'^l 

HIP 

m 

Fig.  153. — Muscles  in  the  Lateral  Wall  of  Larynx. 


deep  portion,  termed  respectively  the  thyro  -  arytenoideus 
externus  and  internus.  These  two  parts  are  as  a  general  rule 
inseparably  united,  and  can  only  be  isolated  from  each  other 
by  artificial  means. 

The  thyro-arytenoideus  externus  is  a  broad  muscular  layer 
which  lies  immediately  subjacent  to  the  ala  of  the  thyroid 
cartilage.  Its  lower  border  is  in  contact  with  the  lateral 
crico-arytenoid  muscle,  whilst  its  upper  border  is  placed  at  a 
higher  level  than  the  true  vocal  cord.  Its  upper  part, 
therefore,   is  in  relation  to  the  wall  of  the  laryngeal  sinus. 


420  HEAD  AND  NECK 

The  thyro-arytenoideus  externus  arises  in  front  from  the 
lower  half  of  the  inner  surface  of  the  ala  of  the  thyroid 
cartilage,  close  to  the  angle,  and  also  from  the  lateral  part 
of  the  crico- thyroid  membrane,  on  which  it  to  some  extent 
lies.  Its  fibres  pass  backwards  and  are  inserted  into  the 
outer  border  and  muscular  process  of  the  arytenoid  cartilage, 
a  certain  number,  however,  turning  round  this  cartilage  and 
becoming  continuous  with  the  arytenoideus  transversus  muscle. 

A  certain  proportion  of  the  uppermost  fibres  of  the  thyro- 
arytenoideus  externus  curve  upwards  and  backwards  to  reach 
the  epiglottis.     These  constitute  the  thyro-epiglottidean  muscle. 

The  thyro-arytenoideus  inter nus  is  a  slender  three -sided 
muscular  band  which  is  closely  applied  to  the  outer  side  of 
the  true  vocal  cord,  and  receives  its  prismatic  form  from  this 
adaptation.  It  arises  in  front  from  the  angular  depression 
between  the  two  alae  of  the  thyroid  cartilage,  and  is  inserted 
behind  into  the  outer  aspect  of  the  processus  vocalis,  and  also 
into  the  adjoining  depressed  part  of  the  antero-external 
surface  of  the  arytenoid  cartilage. 

The  thyro-arytenoideus  internus  is  thicker  behind  than  in 
front.  This  is  due  to  the  fact  that  whilst  all  the  fibres  which 
compose  it  are  attached  to  the  arytenoid  cartilage,  only  a 
certain  proportion  obtain  attachment  to  the  thyroid  cartilage. 
A  large  number  of  the  deeper  fibres  are  directly  attached  at 
different  points  to  the  outer  side  of  the  true  vocal  cord. 
These  constitute  the  ary-vocalis  muscle  (Ludwig). 

A  muscle  termed  the  thyro-arytawideus  superior  is  frequently  present. 
It  is  a  slender  band  which  arises  from  the  inner  aspect  of  the  ala  of  the 
thyroid  cartilage  close  to  the  notch,  and  passes  backwards  and  downwards 
to  find  insertion  into  the  lateral  border  of  the  arytenoid  cartilage  immedi- 
ately above  the  processus  muscularis. 

Dissection. — The  lateral  crico-arytenoid  muscle  should  now  be  carefully 
removed,  and  at  the  same  time  the  dissector  should  endeavour  to  disengage 
the  fibres  of  the  thyro-arytenoideus  externus  from  the  deeper  thyro- 
arytenoideus  internus,  in  order  that  the  relation  of  the  latter  to  the  true 
vocal  cord  may  be  studied.  Finally  remove  the  entire  thyro-arytenoid 
muscle.  This  will  display  the  outer  surface  of  the  lateral  part  of  the  crico- 
thyroid membrane,  the  true  vocal  cord  or  inferior  thyro-arytenoid  ligament, 
and  the  wall  of  the  laryngeal  sinus.  By  carefully  dissecting  between  the 
two  layers  of  mucous  membrane  which  clothe  the  false  vocal  cord,  the 
weak  superior  thyro-arytenoid  ligament  which  gives  it  support  may  be 
discovered,  as  well  as  a  number  of  racemose  glands  which  lie  in  relation 
to  it. 

Lateral  Part  of  the  Crico-thyroid  Membrane. — The  central 
part  of  the  crico-thyroid  membrane,  as  we  have  noted,  closes 


THE  LARYNX 


421 


Muscular  process  of 
arytenoid  cartilage 


in  front  the  interval  between  the  cricoid  and  thyroid  cartilages. 
On  each  side,  however,  the  lateral  part  of  the  same  membrane 
is  not  attached  to  the  lower  border  of  the  thyroid  cartilage, 
but  slopes  upwards  and  inwards,  and  very  materially  diminishes 
the  transverse  width  of  the  lower  subdivision  of  the  laryngeal 
cavity  in  its  upper  part.  The  attachments  which  it  effects 
are  very  definite.  Below,  it  is  fixed  to  the  upper  border  of 
the  cricoid  cartilage,  immediately  subjacent  to  the  mucous 
membrane;  in  front,  it  is  attached  to  the  lower  half  of  the 
inner  surface  of 
the  ala  of  the  thy-  \ 
roid  cartilage,  close 
to  the  angle ;  and 
behind,  to  the  lower 
border  of  the  pro- 
cessus vocalis  of 
the  arytenoid  carti- 
lage. Above,  it  is 
directlycontinuous 
with  the  inferior 
thyro-arytenoid  liga- 
me?it  or  true  vocal 
cord.  The  latter, 
indeed,  may  be 
looked  upon  as 
constituting  its 
upper,  thickened, 
free  border.  In 
contact  with  its 
outer  surface  are 
the  lateral  crico- 
arytenoid and  the  thyro-arytenoid  muscles,  whilst  its  inner 
surface  is  clothed  by  the  lining  mucous  membrane  of  the 
larynx. 

Inferior  Thyro  -  arytenoid  Ligament.  —  This  ligament  is 
formed  in  connexion  with  the  upper  free  border  of  the  lateral 
part  of  the  crico-thyroid  membrane,  and  it  constitutes  the 
support  of  the  true  vocal  cord.  It  is  attached  in  front,  close 
to  its  fellow  of  the  opposite  side,  to  the  middle  of  the  angular 
depression  between  the  two  alae  of  the  thyroid  cartilage.  From 
this  it  stretches  backwards,  and  is  fixed  behind  to  the  tip 
and  upper  border  of  the  processus   vocalis,    which    projects 


Vocal  process  of 
arytenoid  cartilage 


Rima  glotticlis 


Ligament  of  true 
'  vocal  cord 
Lateral  part  of  crico- 
thyroid membrane 
Facet  for  inferior 
cornu  of  thyroid 
cartilage 
-Cricoid  cartilage 


FlG.  154. — Lateral  part  of  Crico-thyroid  Membrane. 
The  right  ala  of  the  thyroid  cartilage  has  been 
removed. 


422  HEAD  AND  NECK 

forwards  from  the  base  of  the  arytenoid  cartilage.  The  in- 
ferior thyro-arytenoid  ligament  is  composed  of  yellow  elastic 
fibres.  Its  inner  border  is  sharp  and  free,  and  is  clothed 
by  mucous  membrane,  which  in  this  position  is  thin  and 
firmly  bound  down  to  the  ligament.  Embedded  in  its 
anterior  extremity  there  is  a  minute  nodule  of  condensed 
elastic  tissue. 

By  removing  the  mucous  membrane  which  lines  the  bottom 
of  the  laryngeal  sinus  the  dissector  will  obtain  a  good  view  of 
the  parts  which  bound  the  rima  glottidis — viz.,  in  front,  the 
angle  of  the  thyroid  cartilage ;  behind,  the  arytenoideus 
transversus  muscle ;  on  each  side,  the  inferior  thyro-arytenoid 
ligament,  the  processus  vocalis,  and  the  inner  surface  of  the 
arytenoid  cartilage  (p.  413).  These  parts  are  clothed  by  the 
lining  mucous  membrane  of  the  larynx. 

Superior  Thyro-arytenoid  Ligament. — This  feeble  band 
supports  the  false  vocal  cord.  It  is  weak  and  indefinite,  but 
somewhat  longer  than  the  preceding  ligament.  In  front  it  is 
attached  to  the  angular  depression  between  the  two  alae  of 
the  thyroid  cartilage,  above  the  true  vocal  cords,  and 
immediately  below  the  attachment  of  the  thyro-epiglottidean 
ligament,  and  extends  backwards  to  be  fixed  to  a  tubercle  on 
the  antero-external  surface  of  the  arytenoid  cartilage  above 
the  processus  vocalis.  It  is  composed  of  connective  tissue 
and  elastic  fibres,  which  are  continuous  with  the  fibrous  tissue 
in  the  aryteno-epiglottidean  fold. 

Dissection. — Remove  the  remains  of  the  aryteno-epiglottidean  fold,  the 
vocal  cords,  and  the  lateral  part  of  the  crico-thyroid  membrane  on  the 
right  side  of  the  larynx,  but  be  careful  not  to  injure  the  arytenoid  cartilage 
and  the  cartilage  of  Santorini.  Should  the  cuneiform  cartilage  be  present 
in  the  aryteno-epiglottidean  fold  it  should  be  detached  and  preserved.  By 
this  dissection  a  closer  view  of  the  side  wall  of  the  laryngeal  cavity  can  be 
obtained.  The  undissected  vocal  cords  of  the  left  side  should  again  be 
examined,  the  laryngeal  sinus  and  pouch  explored,  and  their  precise 
connexions  and  extent  determined.  When  the  student  has  satisfied 
himself  upon  these  points  he  can  proceed  to  display  the  vessels  and  nerves 
of  the  larynx.  The  superior  laryngeal  artery  and  the  internal  laryngeal 
nerve  reach  the  larynx  by  piercing  the  outer  thin  part  of  the  thyro-hyoid 
membrane.  By  applying  traction  to  the  nerve,  and  at  the  same  time 
dividing  the  mucous  membrane  upon  the  inner  surface  of  the  thyro-hyoid 
ligament,  they  can  easily  be  discovered.  In  following  the  branches  into 
which  they  divide,  the  mucous  membrane  must  be  gradually  removed  from 
the  inner  wall  of  the  larynx.  The  inferior  laryngeal  artery  and  nerve  enter 
from  below,  and  proceed  upwards,  under  cover  of  the  ala  of  the  thyroid 
cartilage.  They  can  only  be  satisfactorily  displayed  by  the  removal  of 
this  piece  of  cartilage,  but  the  dissector  is  not  recommended  to  adopt  this 


THE  LARYNX  423 

method  unless  another  larynx  is  available  for  the  examination  of  the 
cartilages  and  joints.  By  drawing  the  thyroid  cartilage  well  outwards  the 
more  important  branches  can  be  studied. 

Internal  Laryngeal  Nerve. — In  the  dissection  of  the  neck 
this  nerve  has  been  observed  to  arise  from  the  superior 
laryngeal  branch  of  the  vagus.  It  is  a  sensory  nerve,  and  its 
branches  are  chiefly  distributed  to  the  mucous  membrane  of 
the  larynx.  Piercing  the  lateral  part  of  the  thyro-hyoid 
ligament,  it  divides  into  three  branches.  The  uppermost  of 
these  sends  filaments  to  the  aryteno-epiglottidean  fold,  to  the 
mucous  membrane  which  covers  the  epiglottis,  and  to  the 
three  folds  in  front  of  it.  The  twigs  which  go  to  the  epiglottis 
ramify  on  its  posterior  surface,  but  many  of  them  pierce  the 
cartilage  to  reach  the  mucous  membrane  on  its  anterior 
surface.  The  intermediate  branch  of  the  internal  laryngeal 
nerve  breaks  up  into  filaments,  wThich  are  given  to  the  mucous 
membrane  lining  the  side  wall  of  the  larynx.  The  lowest 
branch  descends  and  gives  filaments  to  the  mucous  membrane 
which  covers  the  outer  and  back  aspects  of  the  arytenoid  and 
cricoid  cartilages.  A  well-marked  twig  proceeds  from  this 
branch  and  runs  downwards  upon  the  posterior  aspect  of  the 
cricoid  cartilage  to  join  the  recurrent  laryngeal  nerve. 

Recurrent  Laryngeal  Nerve.  —  The  recurrent  laryngeal 
nerve  has  previously  been  seen  to  arise  from  the  vagus,  and 
it  has  been  traced  in  the  neck  up  to  the  point  where  it 
disappears  under  cover  of  the  lower  border  of  the  inferior 
constrictor  muscle.  It  is  now  observed  to  ascend  upon  the 
outer  aspect  of  the  cricoid  cartilage,  immediately  behind  the 
crico-thyroid  joint.  Here  it  is  joined  by  the  communicating 
twig  from  the  internal  laryngeal  nerve,  and  almost  immediately 
afterwards  it  divides  into  two  branches.  The  larger  of  these 
proceeds  upwards  under  cover  of  the  ala  of  the  thyroid 
cartilage,  and  breaks  up  into  filaments  which  supply  the 
lateral  crico-arytenoid,  the  thyro-arytenoid,  and  the  thyro-ary- 
epiglottidean  muscles  ;  the  smaller  or  posterior  branch  inclines 
upwards  and  backwards  upon  the  posterior  aspect  of  the 
cricoid  cartilage,  and  under  cover  of  the  posterior  crico- 
arytenoid muscle.  It  supplies  twigs  to  this  muscle,  and  is 
then  continued  onwards  to  end  in  the  arytenoid  muscle. 

The  recurrent  laryngeal  nerve  is  therefore  the  motor  nerve 
of  the  larynx.  It  supplies  all  the  muscles  with  the  exception 
of  the  crico-thyroid,  which  draws  its  nerve-supply  from  the 


424  HEAD  AND   NECK 

external  laryngeal.  The  recurrent  laryngeal  nerve,  however, 
is  usually  considered  to  contain  a  few  sensory  fibres.  These 
it  gives  to  the  mucous  membrane  of  the  larynx  below  the 
rima  glottidis. 

Laryngeal  Arteries.  —  The  superior  laryngeal  artery r,  a 
branch  of  the  superior  thyroid,  accompanies  the  internal 
laryngeal  nerve  ;  the  inferior  laryngeal  artery  which  springs 
from  the  inferior  thyroid  accompanies  the  recurrent  laryngeal 
nerve.  These  two  vessels  ramify  in  the  laryngeal  wall  and 
supply  the  mucous  membrane,  glands,  and  muscles. 

Laryngeal  Cartilages  and  Joints. — The  cartilages  which 
constitute  the  skeleton  of  the  larynx  and  give  support  to  its 
wall  are  the  following  : — 

T,  t    . ,  .  4.   Arytenoid, 

"   ^  )    .,  '  !»•   Cornicula  laryngis 

2.   Cricoid,  I  .     ,             J                   *-i              rl      •     1 

~    ..,    '       r  .,  r  single.  or    cartilages    off  paired. 

2.   Cartilage  of  the  &  c     *.     •    • 

J           .   7°..  I  hantonni, 

epiglottis,  J  <■     ~       ■(■ 

1  °          '  J  0.   Cuneiform,              J 

They  are  held  together  by  certain  ligaments  and  joints. 

Dissection.  —  The  mucous  membrane  and  muscles  must  be  carefully 
removed  from  the  cartilages,  and  the  epiglottidean,  crico-thyroid,  and 
crico- arytenoid  ligaments  defined.  Great  caution  must  be  exercised  in 
cleaning  the  arytenoid  cartilages  and  the  cartilages  of  Santorini,  in  order 
that  the  latter  may  not  be  injured. 

Cartilage  of  the  Epiglottis  (cartilago  epiglottica). — This  is 
a  thin  leaf-like  lamina  of  yellow  nbro-cartilage  which  is  placed 
behind  the  tongue  and  the  body  of  the  hyoid  bone  and  in 
front  of  the  upper  aperture  of  the  larynx.  When  divested  of 
the  mucous  membrane  which  covers  it  behind  and  also  to 
some  extent  in  front,  the  epiglottidean  cartilage  is  seen  to 
present  the  form  of  a  bicycle-saddle  and  to  be  indented  by  pits 
and  pierced  by  numerous  perforations.  In  the  former,  glands 
are  lodged ;  whilst  through  the  latter,  vessels,  and  in  some 
cases  nerves,  pass.  The  broad  end  of  the  cartilage  is  directed 
upwards  and  is  free  ;  its  margins  are  to  a  large  extent  enclosed 
within  the  aryteno-epiglot.tidean  folds.  The  anterior  surface 
is  only  free  in  its  upper  part.  This  part  is  covered  by  mucous 
membrane  and  looks  towards  the  base  of  the  tongue.  The 
posterior  surface  is  covered  throughout  its  whole  extent  by 
the  mucous  membrane  of  the  larynx.  The  pointed  lower 
end  of  the  cartilage  is  carried  downwards  in  the  form  of  a 
stout  fibrous  band,  termed  the  thyro-epiglottidean  ligament. 

Epiglottidean    Ligaments.  —  The   epiglottis   is   bound   by 


THE  LARYNX  425 

ligaments  to  the  base  of  the  tongue,  to  the  side  wall  of  the 
pharynx,  to  the  hyoid  bone,  and  to  the  thyroid  cartilage.  The 
glosso-epiglottidea?i  fold  and  the  two  pharyngo-epiglottidean  folds 
have  already  been  studied.  In  each  there  is  a  small  quantity 
of  elastic  tissue.  The  hyo-epiglottidean  ligament  is  a  short, 
broad  elastic  band  which  connects  the  anterior  face  of  the 
epiglottis  to  the  upper  border  of  the  body  of  the  hyoid  bone. 
The  thyro-epiglottidea?i  ligame?it'\s  strong,  elastic,  and  thick.  It 
proceeds  downwards  from  the  lower  pointed  extremity  of  the 
epiglottis,  and  is  attached  to  the  angular  depression  between 
the  two  alae  of  the  thyroid  cartilage,  below  and  behind  the 
median  notch. 

The  triangular  interval  which  is  left  between  the  lower 
part  of  the  cartilage  of  the  epiglottis  and  the  thyro-hyoid 
membrane  contains  a  pad  of  soft  fat,  and  is  imperfectly  closed 
above  by  the  hyo-epiglottidean  ligament. 

Thyroid  (cartilago  thyreoidea). — This  is  the  largest  of  the 
laryngeal  cartilages.  It  is  composed  of  two  broad  somewhat 
quadrilateral  plates,  termed  the  alee,  which  meet  in  front  at 
an  angle,  and  become  fused  along  the  mesial  plane.  Behind, 
the  alae  diverge  from  each  other,  and  enclose  a  wide  angular 
space  which  is  open  behind.  The  a?iterior  borders  of  the  alae 
are  only  fused  in  their  lower  parts.  Above  they  are  separated 
by  a  deep,  narrow  V-shaped  notch  called  the  incisura  thyreoidea. 
In  the  adult  male  the  angle  formed  by  the  meeting  of  the 
anterior  borders  of  the  two  alae,  especially  in  the  upper  part, 
is  very  projecting,  and  with  the  margins  of  the  thyroid  notch, 
which  lies  above,  constitutes  a  marked  subcutaneous  prominence 
in  the  neck,  which  receives  the  name  of  the  pomutn  Adami. 
The  posterior  border  of  each  ala  is  thick  and  rounded,  and  is 
prolonged  beyond  the  superior  and  inferior  borders  in  the 
form  of  two  slender  cylindrical  processes  termed  the  cornua. 
The  superior  coma  is  longer  than  the  inferior  cornu,  and  gives 
attachment  to  the  lateral  thyro-hyoid  ligament.  The  shorter, 
stronger  inferior  cornu  curves  slightly  inwards.  On  the  inner 
aspect  of  its  tip  there  is  a  facet  which  articulates  with  the  side 
of  the  cricoid  cartilage.  The  superior  border  of  the  ala  is  for 
the  most  part  slightly  convex,  and  in  front  it  dips  down  to 
become  continuous  with  the  margin  of  the  thyroid  notch. 
The  inferior  border  is  to  all  intents  and  purposes  horizontal, 
but  it  is  marked  off  by  a  projection,  termed  the  i?iferior 
tubercle,  into  a  short  posterior  part  and  a  longer  anterior  part. 


426 


HEAD  AND  NECK 


The  outer  surface  of  the  ala  is  flat.  Immediately  below  the 
posterior  part  of  the  upper  border  and  in  front  of  the  root  of 
the  superior  cornu  there  is  a  distinct  prominence  called  the 
superior  tubercle.  From  this  an  oblique  ridge  descends  towards 
the  inferior  tubercle  on  the  lower  border  of  the  ala.  This 
ridge  gives  attachment  to  the  sterno- thyroid  and  thyro- 
hyoid muscles,  and  divides  the  outer  surface  of  the  ala  into 


Hyoid 


Epiglottis 


Cartilago  triticea 

Thyrohyoid  membrane 

Superior  cornu  of 
thyroid  cartilage 


Thyroid  notch 


Pomum  Adami 

Middle  part  of 
crico-thyroid  membrane' 


Inferior  cornu  of  thyroid 
Cricoid  cartilage 


FIG. 


-Cartilages  and  Ligaments  of  Larynx  viewed  from  the  front. 


an  anterior  and  a  posterior  part.  To  the  latter,  which  is 
much  the  smaller  of  the  two,  is  attached  the  inferior  constrictor 
muscle  of  the  pharynx.  The  inner  surface  of  the  ala  is  smooth 
and  slightly  concave.  To  the  angular  depression  between 
the  two  alae  are  attached  the  thyro-epiglottidean  ligament,  the 
superior  thyro- arytenoid  ligaments,  and  the  inferior  thyro- 
arytenoid ligaments. 

Crico-thyroid  Joints. — The  articulation  on  each  side 
between  the  tip  of  the  inferior  cornu  of  the  thyroid  cartilage 
and    the    side    of    the    cricoid    cartilage,    belongs    to    the 


THE  LARYNX 


427 


diarthrodial  variety.  The  opposed  surfaces  are  surrounded 
by  a  capsular  ligament  which  is  lined  by  a  synovial  membrane. 
The  movements  which  take  place  at  these  joints  are  of  a 
twofold  character — viz.,  (1)  gliding;  (2)  rotatory.  In  the 
first  case  the  thyroid  facets  glide  upon  the  cricoid  surfaces  in 
different  directions.  The  rotatory  movement  is  one  in  which 
the  thyroid  cartilage  rotates  around  a  transverse  axis  which 
passes  through  the 
centre  of  the  two 
joints.  The  capsular 
ligament  is  strength- 
ened by  a  stout  band 
on  the  posterior 
aspect  of  the  joint. 


-  Hyoid 


—  Cartilago  triticea 

Thyrohyoid 

membrane 


Superior  cornu 
of  the  thyroid 
cartilage 


Superior  tubercle 

Oblique  line 
Inferior  tubercle 

Inferior  cornu 
Crico-thyroid 
membrane 
Cricoid  cartilage 


The  thyroid  cartilage 
should  now  be  removed 
by  dividing  the  ligaments 
which  surround  the  crico- 
thyroid joint. 

Cricoid  Cartilage 
(cartilago  cricoidea). 
—  This  is  shaped 
like  a  signet  ring. 
The  broad  posterior 
lamina  is  somewhat 
quadrilateral  in  form. 
Its  superior  border 
presents  a  faintly 
marked  mesial 
notch,  and  on  each 
side  of  this  there  is 
an  oval  convex  facet 
which  articulates 

with  the  base  of  the  arytenoid  cartilage.  The  posterior  surface 
of  the  lamina  is  divided  by  an  elevated  median  ridge  into  two 
slightly  hollowed-out  areas  which  give  attachment  to  the 
posterior  crico-arytenoid  muscles.  The  mesial  ridge  itself  gives 
origin  to  a  tendinous  band  which  proceeds  upwards  from  the 
longitudinal  fibres  of  the  oesophagus.  In  front  of  the 
posterior  lamina  the  ring  of  the  cricoid  cartilage  is  completed 
by  an  anterior  arch.  The  lower  border  of  this  is  horizontal, 
and   is   connected    to   the    first   tracheal    ring   by  membrane. 


Fig.  156.  —  Profile  view  of  Cartilages  and 
Ligaments  of  Larynx. 


428 


HEAD  AND  NECK 


The  arch  is  narrow  in  front,  and  is  attached  to  the  lower 
border  of  the  thyroid  cartilage  by  the  middle  portion  of 
the  crico- thyroid  membrane.  Behind,  the  upper  border 
rapidly  ascends.  Upon  the  posterior  part  of  the  lateral  sur- 
face of  the  cricoid  cartilage  there  is  a  circular,  slightly 
elevated,   convex   facet,   which   looks  outwards  and  upwards 


Cartilago  triticea 

Thyro-epiglotticlean 
ligament 

Superior  cornu 


Cartilage  of  Santorini 

Arytenoid 

Muscular  process 
of  arytenoid 

Inferior  cornu 
of  thyroid 


Fig.   157. — Cartilages  and  Ligaments  of  Larynx  as  viewed  from  behind. 

for  articulation  with  the  inferior  cornu  of  the  thyroid  cartilage. 
Internally  the  cricoid  cartilage  is  lined  by  mucous  membrane. 
Inferiorly  the  lumen  is  circular,  but  above  it  is  elliptical. 

The  narrow  band-like  part  of  the  anterior  arch  of  the 
cricoid  cartilage  lies  below  the  lower  border  of  the  thyroid 
cartilage,  whilst  the  posterior  lamina  is  received  into  the 
interval  between  the  posterior  portions  of  the  alae  of  the 
thyroid  cartilage.    . 


THE  LARYNX  429 

Cartilages  of  Santorini  (cartilagines  corniculatae). — Before 
proceeding  to  the  study  of  the  arytenoid  cartilages  the  dis- 
sector should  examine  the  cartilages  of  Santorini  and  the 
manner  in  which  they  are  held  in  position.  They  are  two 
minute  pyramidal  nodules  of  yellow  elastic  cartilage  which 
are  placed  on  the  summits  of  the  arytenoid  cartilages,  and  are 
directed  backwards  and  inwards.  Each  cartilage  of  Santorini 
is  enclosed  within  the  corresponding  aryteno-epiglottidean 
fold  of  mucous  membrane,  and  is  joined  to  the  apex  of  the 
arytenoid  cartilage  by  a  joint  which  may  either  partake  of  the 
nature  of  diarthrosis  or  synchondrosis. 

Arytenoid  Cartilages  (cartilagines  arytaenoideae). — In  deal- 
ing with  the  arytenoid  cartilages  it  is  well  to  remove  one  in 
order  that  its  external  form  may  be  studied ;  the  other  should 
be  retained  in  position  for  the  purpose  of  afterwards  examin- 
ing the  crico-arytenoid  joint,  and  the  movements  which  can 
be  performed  at  this  articulation. 

The  arytenoid  cartilages  are  pyramidal  in  form,  and  sur- 
mount the  upper  border  of  the  posterior  lamina  of  the  cricoid 
cartilage.  The  apex  of  each  is  directed  upwards,  and  at  the 
same  time  curved  backwards  and  inwards.  It  supports  the 
cartilage  of  Santorini.  Of  the  three  surfaces,  one  looks 
directly  inwards  towards  the  corresponding  surface  of  the 
opposite  cartilage,  from  which  it  is  separated  by  a  narrow 
interval ;  another  looks  backwards ;  whilst  the  third  is 
directed  outwards  and  forwards.  The  internal  surface  is 
narrow,  vertical,  and  even,  and  is  clothed  by  mucous  mem- 
brane. The  posterior  surface  is  concave  ;  it  lodges  and  gives 
attachment  to  the  arytenoideus  transversus  muscle.  The 
antero-external  surface  is  the  most  extensive  of  the  three,  and 
is  uneven  for  muscular  and  ligamentous  attachments.  Upon 
this  aspect  of  the  arytenoid  cartilage  the  thyro-arytenoid 
muscle  is  inserted,  whilst  a  small  tubercle  placed  a  short 
distance  above  the  base  gives  attachment  to  the  superior 
thyro-arytenoid  ligament — the  supporting  ligament  of  the 
false  vocal  cord.  The  surfaces  of  the  arytenoid  cartilage  are 
separated  by  three  borders,  viz.,  an  anterior,  a  posterior,  and 
an  external.  The  external  border  is  the  longest,  and  at  the 
base  of  the  cartilage  it  is  prolonged  outwards  and  backwards 
in  the  form  of  a  stout  prominent  angle  or  process,  termed 
the  processus  muscularis.  Into  the  front  of  this  the  crico- 
arytenoideus  lateralis   muscle  is  inserted ;    into  its   posterior 


430  HEAD  AND  NECK 

aspect  the  crico-arytenoideus  posticus  muscle  is  inserted.  The 
anterior  border  of  the  arytenoid  cartilage  is  prolonged  into 
the  projecting  anterior  angle  of  the  base.  This  is  called 
the  processus  vocalis.  It  is  sharp  and  pointed,  is  directed 
horizontally  forwards,  and  gives  attachment  to  the  inferior 
thyro-arytenoid  ligament  or  true  vocal  cord.  The  base  of  the 
arytenoid  cartilage  presents  an  elongated  concave  facet  on  its 
under  aspect  for  articulation  with  the  upper  border  of  the 
posterior  lamina  of  the  cricoid  cartilage. 

Crico -arytenoid  Joints. — These  articulations  are  of  the 
diarthrodial  variety.  There  is  a  distinct  joint  cavity  sur- 
rounded by  a  capsular  ligament  which  is  lined  by  a  synovial 
membrane.  The  cricoid  articular  surface  is  convex,  that  of 
the  arytenoid  concave ;  both  are  elongated  in  form,  but  they 
are  placed  in  relation  to  each  other,  so  that  the  long  axis  of 
the  one  intersects  or  crosses  that  of  the  other,  and  in  no 
position  of  the  joint  do  the  two  surfaces  accurately  coincide ; 
a  portion  of  the  cricoid  surface  is  always  left  uncovered. 
The  movements  allowed  at  this  joint,  as  the  dissector  can 
readily  determine,  are  of  a  twofold  kind — (i)  gliding,  by 
which  the  arytenoid  is  carried  inwards  or  outwards,  or,  in 
other  words,  a  movement  by  which  the  arytenoid  advances 
towards  or  retreats  from  its  fellow;  (2)  rotatory,  by  which  the 
arytenoid  cartilage  revolves  round  a  vertical  axis.  By  this 
movement  the  vocal  process  is  swung  outwards  or  inwards,  so 
as  to  open  or  close  the  rima  glottidis. 

The  dissector  should  note  that  the  capsule  of  this  joint 
is  strengthened  behind  by  a  strong  band  which  plays  a  most 
important  part  in  the  mechanism  of  the  articulation.  It  acts 
in  such  a  manner  that  it  arrests  forward  movement  of  the 
arytenoid  cartilage. 

Cuneiform  Cartilages  (cartilagines  cuneiformes). — These 
are  two  little  rod-shaped  nodules  of  yellow  elastic  cartilage, 
which  are  placed  one  in  each  aryteno-epiglottidean  fold  near 
its  back  part.     They  are  not  always  present. 

Action  of  the  Laryngeal  Muscles.  — The  dissector  should  now  consider 
the  manner  in  which  the  muscles  of  the  larynx  operate  upon  the  true  vocal 
cords  in  the  production  of  the  voice.  Tension  of  the  vocal  cords  is  pro- 
duced by  the  contraction  of  the  crico-thyroid  muscles.  The  anterior  or 
oblique  parts  of  the  muscles  pull  the  lower  border  of  the  thyroid  cartilage 
downwards,  whilst  the  posterior  horizontal  portions,  through  their  insertions 
into  the  inferior  cornua,  draw  the  thyroid  cartilage  forwards,  thereby 
increasing   the  distance  between  the  angle  of  the  thyroid  cartilage  and 


THE  LARYNX  431 

the  vocal  processes  of  the  arytenoid  cartilages.  When  the  crico-thyroid 
muscles  cease  to  contract,  the  relaxation  of  the  cords  is  brought  about  by 
the  elasticity  of  the  ligaments.  The  thyro-arytenoid  muscles  must  be 
regarded  as  antagonistic  to  the  crico-thyroid  muscles.  "When  they  contract 
they  approximate  the  angle  of  the  thyroid  cartilage  to  the  arytenoid 
cartilages,  and  still  further  relax  the  cords,  and  when  they  cease  to  act, 
the  elastic  ligaments  of  the  larynx  again  bring  about  a  state  of  equilibrium. 
The  ary-vocales  muscles,  by  the  insertion  of  their  fibres  into  the  true  vocal 
cords,  may  tighten  portions  of  the  cords,  and,  at  the  same  time,  relax  the 
parts  behind. 

The  width  of  the  rima  glottidis  is  regulated  by  the  arytenoideus  muscle, 
which  draws  together  the  arytenoid  cartilages.  The  lateral  and  posterior 
crico-arytenoid  muscles  also  modify  the  width  of  the  rima  glottidis.  When 
they  act  together  they  assist  the  arytenoid  muscle  in  closing  the  glottis, 
but  when  they  act  independently  they  are  antagonistic  muscles.  Thus  the 
crico-arytenoidei  postici,  by  drawing  the  muscular  processes  of  the  arytenoid 
cartilages  outwards  and  backwards,  swing  the  processus  vocales  and  the 
vocal  cord  outwards,  and  thus  open  the  rima.  The  crico-aiytenoidei 
laterales  act  in  exactly  the  opposite  manner.  By  drawing  the  muscular 
processes  in  an  opposite  direction,  they  close  the  rima. 

But  the  muscles  of  the  larynx  have  another  function  to  perform  besides 
that  of  vocalisation.  It  was  formerly  thought  that  the  superior  aperture 
of  the  larynx  was  closed  during  deglutition  by  the  folding  back  of  the 
epiglottis  ;  that  in  fact  the  epiglottis,  during  the  passage  of  the  bolus  of 
food,  was  applied  like  a  lid  over  the  entrance  to  the  vestibule  of  the  larynx. 
The  investigations  of  Prof.  Anderson  Stuart,  however,  have  rendered  it 
likely  that  the  superior  aperture  of  the  larynx  is  closed  during  swallowing 
by  the  close  application  and  the  forward  folding  of  the  two  arytenoid 
cartilages,  so  that  their  apices  become  closely  applied  to  the  cushion  of 
the  epiglottis.  The  muscles  chiefly  concerned  in  this  movement  are  the 
external  thyro-arytenoid  muscles  and  the  transverse  arytenoid  muscle. 
These  muscles  form  a  true  sphincter  vestibuli.  The  thyro-ary-epiglottidean 
muscle  also  assists  in  the  closure. 


THE  TONGUE. 

The  tongue  is  a  muscular  organ  placed  on  the  floor  of 
the  mouth.  It  has  important  duties  to  perform  in  connexion 
with  the  functions  of  mastication,  deglutition,  and  articulation. 
Moreover,  the  mucous  membrane  which  covers  it  is  specially 
modified  in  certain  localities  in  connexion  with  the  peripheral 
terminations  of  the  nerves  of  taste.  The  root  of  the  tongue 
is  attached  to  the  hyoid  bone ;  in  front,  the  pointed  extremity 
is  free ;  whilst  the  dorsal  aspect  of  its  base  forms  the  lower 
boundary  of  the  isthmus  faucium. 

Mucous  Membrane. — The  lingual  mucous  membrane  is 
a   part  of  the  general   mucous    lining   of  the   buccal   cavity. 


432  HEAD  AND   NECK 

The  dorsum  of  the  tongue,  when  the  mouth  is  closed  and 
the  organ  is  at  rest,  is  strongly  arched  from  before  backwards, 
and  for  the  most  part  is  moulded  into  the  vaulted  roof  of 
the  mouth.  The  tongue  consists  of  two  developmentally 
distinct  parts,  termed  respectively  buccal  and  pharyngeal. 
These  are  marked  off  from  each  other,  even  in  the  adult, 
by  a  V-shaped  groove  called  the  sulcus  terminalis.  The 
apex  of  this  sulcus  points  backwards,  and  coincides  with  a 
median  blind  pit  which  receives  the  name  of  the  foramen 
ccecum.  From  this  the  two  limbs  of  the  sulcus  diverge  out- 
wards and  forwards,  and  they  reach  the  margins  of  the  organ 
where  the  anterior  pillars  of  the  fauces  find  attachment  to 
the  tongue. 

The  buccal  part  of  the  tongue,  by  its  upper  or  dorsal 
surface,  stands  in  relation  to  the  hard  palate,  and  to  some 
extent  also  to  the  front  portion  of  the  soft  palate.  The 
pharyngeal  part  of  the  tongue  looks  backwards,  and  forms 
the  anterior  wall  of  the  oral  portion  of  the  pharynx.  In  its 
upper  part  it  is  related  to  the  soft  palate,  whilst  below  it  is 
intimately  related  to  the  epiglottis.  On  the  side  wall  of  the 
pharynx,  immediately  above  this  portion  of  the  tongue,  is 
the  tonsil. 

The  mucous  membrane  which  envelops  the  tongue  is  a 
part  of  the  general  mucous  lining  of  the  buccal  cavity,  and 
it  presents  very  different  appearances  in  different  localities. 
That  portion  which  is  spread  over  the  pharyngeal  part  of 
the  tongue,  and  which  on  either  side  is  prolonged  upwards 
over  the  surface  of  the  tonsil,  exhibits  a  very  characteristic 
appearance.  It  is  smooth  and  somewhat  glossy,  and  pre- 
sents no  visible  papillae.  It  is  from  this  district  that  the 
middle  glosso-epiglottidean  fold  takes  origin,  and  every 
here  and  there  the  surface  is  studded  with  low  projections 
which  are  produced  by  lymphoid  follicles  placed  subjacent 
to  the  mucous  membrane.  Each  of  these  small  elevated 
areas,  as  a  rule,  presents  in  the  centre  a  minute  pit,  visible 
to  the  naked  eye. 

In  front  of  the  foramen  caecum  and  sulcus  terminalis  the 
mucous  membrane  which  covers  the  dorsum,  sides,  and  tip 
of  the  buccal  part  of  the  tongue  is  beset  with  papillae  of 
different  kinds.  As  these  are  individually  visible  to  the  naked 
eye,  the  mucous  membrane  presents  a  very  characteristic 
appearance.      Further,   a  mesial  groove  or  sulcus  called  the 


THE  TONGUE 


433 


raphe  extends  backwards  from  the  tip  of  the  tongue  to  the 
foramen  caecum,  and  divides  the  anterior  two-thirds  of  the 
dorsum  into  two  lateral  parts. 

On  the  under  surface  of  the  tongue  the  mucous  mem- 
brane is  smooth  and  comparatively  thin.  In  the  mesial 
plane  it  forms  the  frenum  lingua,  which  has  been  studied 
at  an  earlier  stage.  On  either  side  of  the  median  line  the 
lingual  vein  may  be  noticed  in  the  living  subject  stretching 
forwards  towards  the  tip.  To  the  outer  side  of  this,  and, 
therefore,   somewhat  nearer  the  border  of  the   tongue,    is  a 


Tip  of  tongue 
turned  up" 


Ranine  vein- 


Orifice  of 
Wharton's  duct" 


Frenum  linguae 
Plica  fimbriata 

Plica  sublingualis 


FlG.  158. — The  Sublingual  Region  in  the  Interior  of  the  Mouth. 

delicate  and  feebly  marked  fold  of  mucous  membrane,  from 
the  free  border  of  which  a  row  of  fringe-like  processes  or 
fimbriae  project.  It  is  termed  the  plica  fimbriata,  and,  as  it 
extends  forwards  towards  the  tip  of  the  tongue,  it  inclines 
towards  the  mesial  plane  and  its  neighbour  of  the  opposite 
side.  On  the  side  of  the  tongue,  immediately  in  front  of 
the  lingual  attachment  of  the  anterior  pillar  of  the  fauces, 
five  short  vertical  fissures  in  the  mucous  membrane,  separated 
by  intervening  folds,  may  be  noticed.  This  arrangement  is 
termed  the  papilla  foliata.  It  is  the  representative  of  a  leaf- 
like condition  of  the  mucous  membrane,  which  is  much  more 
highly  developed  in  certain  of  the  lower  animals  (hare  and 
vol.  11 — 28 


434  HEAD  AND  NECK 

i 
rabbit),   and   which    is  specially  concerned   in    receiving   the 
impressions  of  taste. 

Lingual  Papillae  (papillae  linguales). — These  are  of  three 
kinds,  and  differ  in  size,  shape,  and  in  the  position  they 
occupy  on  the  surface  of  the  tongue.  They  are  termed  the 
circumvallate,  the  fungiform,  and  the  conical. 

The  circumvallate  papillce  (papillae  vallatae),  seven  to  twelve 
in  number,  are  the  largest,  and  are  placed  immediately  in 
front  of  the  sulcus  terminalis  in  two  rows,  which  diverge 
from  each  other  in  an  outward  and  forward  direction,  like 
the  two  limbs  of  the  letter  V-  The  foramen  caecum  lies 
immediately  behind  the  median  circumvallate  papilla,  which 
forms  the  apex  of  the  V.  In  form  a  circumvallate  papilla 
is  broad  and  somewhat  cylindrical,  slightly  narrower  at  its 
attached  than  at  its  free  extremity,  and  it  is  sunk  in  a  pit. 
It  is  thus  surrounded  by  a  deep  trench,  the  outer  wall  01 
which,  termed  the  vallum,  is  slightly  raised  beyond  the  general 
surface  of  the  mucous  membrane,  and  forms  an  annular  eleva- 
tion which  encircles  the  free  extremity  or  summit  of  the 
papilla. 

The  fungiform  papillce  (papillae  fungiformes)  are  much 
smaller,  but  are  present  in  much  greater  numbers.  They  are 
chiefly  found  on  the  tip  and  sides  of  the  tongue,  but  they  are 
also  scattered  at  irregular  intervals  over  the  dorsum.  They 
are  very  characteristic  in  form.  Each  papilla  presents  a 
large,  full,  rounded  knob-like  extremity,  while  it  is  greatly 
constricted  at  the  point  where  it  springs  from  the  mucous 
surface.  In  the  living  tongue  the  fungiform  papillae  are 
distinguished  by  their  bright  red  colour. 

The  conical  papillce  (papillae  conicae)  are  present  in  very 
large  numbers.  They  are  smaller  than  the  fungiform  variety, 
and  although  they  are  quite  visible  to  the  naked  eye,  they 
can  be  more  conveniently  studied  by  the  aid  of  an  ordinary 
pocket  lens.  They  are  minute  conical  projections  which 
taper  towards  their  free  extremities,  and  occupy  the  dorsum 
and  sides  of  the  tongue  in  front  of  the  sulcus  terminalis. 
They  are  arranged  in  parallel  rows  which  are  placed  close 
together,  and  in  the  back  part  of  the  tongue  these  diverge 
from  the  mesial  raphe  in  a  forward  and  outward  direction. 
Towards  the  tip  of  the  tongue  the  rows  of  conical  papillae 
become  more  or  less  transverse  in  direction,  and  on  the  sides 
of  the  tongue  they  are  arranged  perpendicularly. 


THE  TONGUE 


435 


Muscles  of  the  Tongue. — The  tongue  is  almost  entirely 
composed  of  muscular  fibres,  with  some  adipose  tissue  inter- 
mixed. It  is  divided  into  two  lateral  halves  by  a  mesial 
septum,  and  the  muscles  in  connexion  with  each  of  these 
consist  of  an  intrinsic  and  an  extrinsic  group.  They  are  as 
follows  : — 


Extrinsic  Muscles, 


Intrinsic  Muscles, 


It 

fi 

I3- 

I  4- 


Genio-hyo-glossus. 

Hyo-glossus. 

Chondro-glossus. 

Styloglossus. 

Palatoglossus. 

Superficial  lingual. 

Inferior  lingual. 

Vertical. 

Transverse. 


Posterior  belly 
of  digastric 


Anterior  belly  of  digastric  Mylo-hyoid         Genio-hyoid 

Fig.  159. — Muscles  of  the  Tongue.     (From  Gegenbaur. ) 

The  extrinsic  muscles  take  origin  from  parts  outside  the 
tongue,  and  thus  are  not  only  capable  of  giving  rise  to 
changes  in  the  form  of  the  organ,  but  also  of  producing 
changes  in  its  position.  The  intrinsic  muscles,  which  are 
placed  entirely  within  the  substance  of  the  tongue,  are,  for 
the  most  part,  only  capable  of  giving  rise  to  alterations  in 
its  form. 

With  the  exception  of  the  chondro-glossus,  the  extrinsic  muscles  have 

already  been   studied,   but   t he  dissector  should   take  this  opportunity  of 

examining  more  fully  their  insertions,  and  the  manner  in  which  their  fibres 

are  related  to  each  other  and  to  those  of  the  intrinsic  muscles.      For  this 

TT — 28  ^ 


43^ 


HEAD   AND   NECK 


purpose  carefully  reflect  the  mucous  membrane  from  the  right  half  of  the 
tongue,  and  follow  the  muscles  into  that  side  of  the  organ.  At  the  same 
time  the  lingual  nerves  and  the  ranine  artery  should  be  preserved.  On  the 
under  surface  of  the  tongue  near  the  tip,  the  removal  of  the  mucous  mem- 
brane will  expose  a  group  of  glands  aggregated  together,  so  as  to  form  a 
small  oval  mass  on  each  side  of  the  mesial  plane.  This  is  known  as  the 
apical  gland  or  the  gland  of  Niihn. 

The  stylo-glossus  will  be  observed  to  run  along  the  side  of 
the  tongue  to  the  tip,  where  the  two  muscles  become  to  a 
certain  extent  continuous.  The  hyo-glossus  extends  upwards 
to  the  side  of  the  tongue,  and  its  fibres  pass  for  the  most  part 
under  cover  of  those  of  the  stylo-glossus  to  reach  the  dorsum, 
over  the  posterior  part  of  which  they  spread  out  beneath  the 
mucous  membrane.  The  genio -hyo-glossus  sends  its  fibres 
vertically  upwards  into  the  tongue  on  each  side  of  the  mesial 


—  Palatoglossus 

ossus 
Septum  linguae 
Lingualis  inferior 
Hyo-glossus 
Genio-glossus 

Fig.  160. — Transverse  section  through  the  hinder  part 
of  the  Tongue.      (From  Gegenbaur. ) 


septum,  and  its  insertion  stretches  from  the  tip  to  the  base. 
The  fibres  of  the  palato-glossus  become  continuous  with  those 
which  form  the  stratum  transversum. 

The  chotidro-glossus  is  not  always  present.  It  is  separated 
from  the  deep  surface  of  the  hyo-glossus  by  the  lingual  vessels, 
and  by  the  pharyngeal  slip  of  the  genio-hyo-glossus.  It  is  a 
slender  muscular  band  which  takes  origin  from  the  inner 
aspect  of  the  root  of  the  lesser  cornu,  and  the  adjoining  part 
of  the  body  of  the  hyoid  bone.  Its  fibres  ascend  to  enter  the 
tongue,  and  finally  spread  out  on  the  dorsum  under  cover  of 
the  lingualis  superior. 

The  superficial  lingual  muscle  (musculus  longitudinalis 
superior)  is  a  continuous  layer  of  longitudinal  fibres  which 
covers  the  entire  dorsum  linguae,  from  the  root  to  the  tip, 
immediately  beneath  the  mucous  membrane.  Towards  the 
base  of  the  tongue  it  is  thinner  than  in  front,  and  here  it  is 


THE  TONGUE 


437 


overlapped  by  the  transverse  fibres  of  the  hyo-glossus,  and  is 
intermixed  with  the  fibres  of  the  chondro-glossus. 

The  inferior  lingual  muscle  (musculus  longitudinalis  inferior) 
is  a  rounded  fleshy  belly  which  is  placed  upon  the  inferior 
aspect  of  the  tongue.  Behind,  it  lies  in  the  interval  between 
the  hyo-glossus  and  the  genio-hyo-glossus,  and  shows  an 
attachment  to  the  hyoid  bone  ;  in  front,  it  is  prolonged  to  the 
apex  of  the  tongue  between  the  inner  border  of  the  stylo- 
glossus and  the  genio-hyo-glossus ;  with  the  former  it  is  more 
or  less  blended. 

The  transverse  muscular  fibres  (musculus  transversus  linguae) 
lie  under  the  lingualis  superior,  and  constitute  a  thick  layer 
which  extends  outwards  from  the  lateral  face  of  the  septum 


—  Lingualis  superior 
^— |— ^Lamella;  of 


Genio-hyo-glussus 

Genio-hyoid 


n 

Hyoid  bone 


stratum  transversum 


Lingualis  inferior 


FlG.  161. — Longitudinal  section  through  the  Tongue. 
(From  Aeby. ) 

linguae,  to  reach  the  dorsum  arid  side  of  the  tongue.  The 
fibres  of  the  genio-hyo-glossus  ascend  through  the  stratum 
transversum  and  break  it  up  into  numerous  lamellae  (Fig. 
161).  It  is  joined  by  the  fibres  of  the  palato  -  glossus 
(Henle)  (Fig.  160). 

The  vertical  muscular  fibres  (musculus  verticalis  linguae) 
extend  in  a  curved  direction  from  the  dorsum  to  the  under 
aspect  of  the  tongue,  and  decussate  with  the  fibres  of  the 
stratum  transversum. 

Nerves  and  Vessels  of  the  Tongue. — The  nerves  of  the 
tongue  are — (i)  the  glosso-pharyngeal ;  (2)  the  lingual;  (3) 
the  hypoglossal ;  and  (4)  a  few  twigs  from  the  internal 
laryngeal.  These  should  be  traced  on  the  left  side  of  the 
tongue,  where  the  mucous  membrane  is  still  in  position. 

The  glosso-pharyngeal nervehsLS  been  traced  up  to  the  point 
where   it   disappears   under  cover  of  the   hyo-glossus  muscle. 


438 


HEAD  AND  NECK 


Here  it  divides  into  two  branches.  The  smaller  of  these 
extends  forwards  upon  the  side  of  the  tongue,  and  may  be 
traced  as  far  as  a  point  midway  between  the  root  and  the  tip. 
The  larger  branch  turns  upwards  and  is  distributed  to  the 
mucous  membrane  which  invests  the  posterior  third  of  the 
dorsum  linguae.  It  gives  twigs  to  the  circumvallate  papillae, 
and  some  fine  filaments  may  be  followed  to  the  anterior  surface 
of  the  epiglottis.  The  glosso-pharyngeal  nerve  is  the  principal 
nerve  of  taste. 

The  lingual  and  hypoglossal  nerves  are  described  in  pages 
302  and  303,  and  their  terminal  branches  should  now  be 
traced  as  far  as  it  is  possible  to  do  so. 

The  internal  laryngeal  nerve  gives  a  few  delicate  filaments 

to  the  glosso-epiglot- 

Linguaiis  superior^   ^  ,.„. ^ tidean  folds  and  the 

mucous     membrane 
%  of   the    root    of   the 
tongue. 


Stratum 
transversunT 


Stylo-glossus- 


Lingualis  inferior^     -^ 
Hyo-glossus 
Genio-glossus 


The  ranine  artery 
should  be  followed 
to  the  tip  of  the 
tongue,  where  it 
forms  a  small  loop 
of  anastomosis  with 
its  fellow  of  the  op- 
posite side  (p.  305). 
Septum  Linguae. — The  septum  of  the  tongue  can  best  be 
seen  by  making  a  transverse  section  through  the  organ. 
This  will  also  in  a  measure  demonstrate  the  transverse  and 
perpendicular  muscular  fibres.  The  septum  is  a  mesially 
placed  fibrous  partition.  It  is  strongest  behind,  where  it  is 
attached  to  the  hyoid  bone. 


Hyoid  bone         Geniohyoid 


Fig.  162. — Transverse  section  through  the 
Tongue.       (From  Aeby. ) 


GENERAL  APPEARANCE  OF  BRAIN  439 


THE   BRAIN. 

Directions. — In  the  first  instance  the  brain  should  be  placed  on  a 
dissecting-room  platter,  with  its  superior  surface  uppermost.  It  is  neces- 
sary to  keep  it  moist  during  the  whole  dissection,  by  means  of  a  cloth 
dipped  in  water.  Unless  this  be  done  the  membranes  are  apt  to  become 
dry,  and  then  they  are  exceedingly  difficult  to  remove. 

General  Appearance  of  the  Brain. — When  viewed  from 
above,  the  brain  presents  an  ovoid  figure,  its  broad  end  being 
directed  backwards.  Its  greatest  transverse  diameter  is  in 
the  neighbourhood  of  that  part  which  lies  between  the  two 
parietal  eminences  of  the  cranium.  The  only  parts  which 
are  visible  when  the  brain  is  in  this  position  are  the  two 
convoluted  cerebral  hemispheres.  These  are  separated  from 
each  other  by  a  deep  mesial  cleft,  called  the  great  longitudinal 
fissure,  which  extends  from  the  front  to  the  back  of  the  brain. 

The  position  of  the  brain  should  now  be  reversed.  Turn  it  so  that  it 
rests  on  its  superior  surface. 

The  inferior  aspect  of  the  brain  is  usually  termed  the 
"  base."  It  presents  an  uneven  and  irregular  surface,  which 
is  more  or  less  accurately  adapted  to  the  inequalities  on  the 
floor  of  the  cranium.  From  this  point  of  view  some  of  the 
main  subdivisions  of  the  organ  may  be  recognised.  Thus, 
behind  is  seen  the  short  cylindrical  portion,  called  the  medulla 
oblongata  or  bulb,  through  which,  at  the  foramen  magnum, 
the  brain  becomes  continuous  with  the  spinal  cord.  The 
bulb  rests  on  the  under  surface  of  the  cerebellum,  being 
received  into  the  vallecula  or  hollow  which  intervenes  between 
the  two  cerebellar  hemispheres.  The  cerebellum  is  a  mass  of 
considerable  size  which  lies  under  the  hinder  portions  of  the 
cerebral  hemispheres.  It  can  be  easily  recognised  on  account 
of  the  closely  set,  curved  and  parallel  fissures  which  traverse 
its  surface.  Above  the  medulla,  and  in  direct  connexion 
with  it,  is  a  prominent  white  elevation  called  the  pons  Varolii. 
The  basilar  artery  extends  upwards  in  a  mesial  groove  on  its 
surface.  Immediately  in  front  of  the  pons  Varolii  there  is  a 
deep  hollow  or  recess.  This  is  bounded  behind  by  the  pons, 
on  either  side  by  the  projecting  temporal  lobes  of  the 
cerebrum,  and  in  front  by  the  orbital  portions  of  the  frontal 

n—28// 


44° 


THE  BRAIN 


lobes  of  the  cerebrum.  At  the  present  stage  of  the  examina- 
tion of  the  brain,  the  bottom  of  this  hollow  is  hidden  from 
view  by  the  arachnoid  mater,  which  stretches  over  it  like  a 

Optic  chiasma 

\ 


Infundibulum 


Corpora 
mammillaria 


Locus 

perforatus 

posticus 


Crus 
cerebri 


Olfactory  bulb 


Sixth 
nerve 


Hypoglossal 
nerve 


Pyramid 
Spinal  cord  (cut) 


Olfactory  tract 


Optic  nerve 

Locus  perfor- 
atus anticus 


Optic  tract 


Tuber 
cinereum 

Third  nerve 


Fourth  nerve 
Fifth  nerve 


Facial  nerve 
Auditory  nerve 

Pars  intermedia 

Glosso-pharyngeal 
nerve 

Vagus  nerve 
Spinal  accessory  nerve 

Hypoglossal  nerve 


Fig.  163. — The  Base  of  the  Brain  with  the  Cranial  Nerves  attached. 

veil ;  but  if  the  pituitary  body  has  been  removed  with  the 
brain  it  will  be  seen  within  its  limits.  Passing  out  from  either 
side  of  the  fore-part  of  this  recess  will  be  seen  the  deep 
Sylvian  fissure,  which  intervenes  between  the  pointed  and 
projecting  extremity  of  the  temporal  lobe  and  the  frontal  lobe 


GENERAL  APPEARANCE  OF  BRAIN         441 

of  the  cerebrum ;  whilst  in  the  middle  line  in  front  the  great 
longitudinal  fissure  will  be  observed  to  separate  the  frontal 
portions  of  the  cerebral  hemispheres.  On  either  side  of  the 
great  longitudinal  fissure,  and  separated  from  it  by  a  narrow 
gyrus,  the  olfactory  peduncle  and  bulb  may  be  recognised. 


MEMBRANES  AND  BLOOD  VESSELS  OF 
THE  BRAIN. 

Arachnoid  Mater  (arachnoidea  encephali). — This  forms 
the  intermediate  covering  of  the  brain.  Placed  between  the 
dura  mater  and  the  pia  mater,  it  is  directly  continuous  with 
the  arachnoidea  of  the  spinal  cord.  It  is  an  exceedingly 
thin  and  delicate  membrane,  which  can  best  be  seen  on  the 
base  of  the  brain,  as  in  this  locality  it  is  not  so  closely  applied 
to  the  pia  mater  as  elsewhere.  Unlike  the  pia  mater,  it  does 
not  (except  in  the  case  of  the  great  longitudinal  and  the 
Sylvian  fissures)  dip  into  the  sulci  on  the  surface  of  the 
cerebrum  and  cerebellum.  It  bridges  over  the  inequalities 
on  the  surface  of  the  brain.  It  is  consequently  spread  out 
in  the  form  of  a  very  distinct  sheet  over  the  medulla,  the  pons 
Varolii,  and  the  hollow  on  the  base  of  the  brain  which  lies  in 
front  of  the  pons.  The  cut  ends  of  several  of  the  cranial 
nerves  will  be  observed  projecting  through  this  sheet ;  whilst 
in  front,  immediately  to  the  outer  side  of  the  optic  nerve,  the 
internal  carotid  artery  may  be  noticed  piercing  it. 

Subarachnoid  Space  (cavum  subarachnoidale). — The  in- 
terval between  the  arachnoidea  and  the  pia  mater  receives 
the  name  of  the  subarachnoid  space.  It  contains  the  sub- 
arachnoid fluid,  and  is  broken  up  by  a  meshwork  of  fine 
filaments  and  trabecular,  which  connects  the  two  bounding 
membranes  (viz.,  the  arachnoidea  and  the  pia  mater)  in  the 
most  intimate  manner,  and  forms  a  delicate  sponge-like 
interlacement  between  them.  Where  the  arachnoidea  passes 
over  the  summit  of  a  cerebral  convolution,  and  is  consequently 
closely  applied  to  the  subjacent  pia  mater,  the  meshwork  is 
so  close  and  the  trabecular  so  short  that  the  two  membranes 
cannot  be  separated  from  each  other.  To  the  dissector  they 
appear  to  form  a  single  lamina.  In  the  intervals  between 
the  rounded  margins  of  adjacent  convolutions,  distinct  angular 


44- 


THE  BRAIX 


spaces  exist  between  the  arachnoidea  and  the  pia  mater.  In 
these  the  subarachnoid  tissue  can  be  studied,  and  it  will  be 
seen  that  by  these  intervals  on  the  surface  of  the  cerebrum, 
numerous  communicating  channels  are  formed  which  serve 
for  the  free  passage  of  the  subarachnoid  fluid  from  one  part 
of  the  brain  to  another.  The  larger  branches  of  the  arteries 
and  veins  of  the  brain  traverse  the  subarachnoid  space ;  their 
walls  are  directly  connected  with  the  subarachnoid  trabecular, 
and  are  bathed  by  the  subarachnoid  fluid. 

Cisternse    Subarachnoidal.  — In    certain    situations    the 
arachnoidea  is   separated  from  the  pia  mater  by  intervals  of 


Vein 


Sub-arachnoid  space  and  trabeculae 


-  -  Dura  mater 
-Subdural  space 
•Arachnoid  mater 
"Pia  mater 


Fig.  164. — Diagrammatic  section  through  the  Meninges  of 
the  Brain.      (Schwalbe. ) 

co.  Grey  matter  of  cerebral  convolutions. 

considerable  depth  and  extent.  These  expansions  of  the 
subarachnoid  space  are  termed  cisternal  subarachnoidales.  In 
these  the  subarachnoid  tissue  is  greatly  reduced.  There 
is  no  longer  a  close  meshwork ;  the  trabecular  connecting  the 
two  bounding  membranes  take  the  form  of  long  filamentous 
intersecting  threads,  which  traverse  the  spaces.  A  beautiful 
demonstration  of  these  may  be  obtained  by  dividing  in  the 
mesial  plane,  with  the  scissors,  the  sheet  of  arachnoidea  which 
is  spread  over  the  medulla  and  pons,  and  turning  the  two 
pieces  gently  outwards. 

Certain  of  the  cisterns  require  special  mention.  The  largest  and  most 
conspicuous  is  called  the  cisterna  magna.  It  is  a  direct  continuation  of  the 
posterior  part  of  the  subarachnoid  space  of  the  spinal  cord  upwards  into  the 


MEMBRANES  AND  BLOOD  VESSELS 


443 


hinder  part  of  the  cranium.  It  is  formed  by  the  arachnoid  membrane 
bridging  over  the  wide  interval  between  the  back  part  of  the  under  surface 
of  the  cerebellum  and  the  medulla  oblongata. 

The  cistema  pontis  is  the  name  given  to  another  of  these  recesses.  It  is 
the  continuation  upwards  on  the  floor  of  the  cranium  of  the  anterior  part  of 
the  subarachnoid  space  of  the  cord.  In  the  region  of  the  medulla  it  is  con- 
tinuous on  either  side  with  the  cisterna  magna,  so  that  this  subdivision  of 
the  brain  is  completely  surrounded  by  a  wide  subarachnoid  space.  Within 
the  cisterna  pontis  are  the  vertebral  and  basilar  arteries. 

In  front  of  the  pons  Varolii  the  arachnoid  membrane  bridges  across 
between  the  projecting  temporal  iobes,  and  covers  in  the  deep  hollow  in 
this  region  of  the  base  of  the  brain.     This  space  is   called    the  cisterna 


Parasinoidal  sinus 

X 


Pacchionian  body 


Pacchionian  body  y..^ 

w 

Longitudinal  sinus 


Parasinoidal  sinus 


Dura  mater 


Blood  vessels 
Grey  cortex  of  a 


?ia  mater 
Subarachnoid  space 

x  Arachnoid  mater 


I'alx  cerebri 


Fig.  165. — Diagram  of  a  coronal  section  through  the  middle  portion  of  the 
cranial  vault  and  subjacent  brain  to  show  the  membranes  of  the  brain 
and  the  Pacchionian  bodies. 

basalts,  and  within  it  arc  placed  the  large  arteries  which  take  part  in  the 
formation  of  the  circle  of  Willis.  Leading  out  from  the  cisterna  basalis 
there  are  certain  wide  subarachnoid  channels.  Two  of  these  are  prolonged 
into  the  Sylvian  fissures,  and  in  these  are  accommodated  the  middle  cerebral 
arteries  and  some  of  their  branches.  In  front  the  basal  cistern  passes 
into  a  space  in  front  of  the  optic  chiasma,  and  from  this  it  is  continued  into 
the  great  longitudinal  fissure  above  the  corpus  callosum.  In  this  sub- 
arachnoid passage  are  lodged  the  anterior  cerebral  arteries. 

All  the  subarachnoid  cisterns  communicate  in  the  freest  manner  with 
each  other,  and  also  with  the  narrow  intervals  on  the  surface  of  the  cere- 
brum. Th'.-  subarachnoid  space  does  not  communicate  in  any  way  with 
the  subdural  space.  In  certain  localities,  however,  it  communicates  with 
the  ventricular  system  of  the  brain.  Three  such  apertures  are  described  in 
connexion  with  the-  fourth  ventricle,  whilst  anothci  slit  is  said  to  lead  from 
the  cisterna  ba  >alis  into  the  lower  end  of  the  descending  horn  of  the  lateral 
ventricle. 


Pacchionian  Bodies. — The  connexion  of  the   Pacchionian 


444  THE  BRAIN 

bodies  with  the  arachnoid  mater  has  already  been  referred  to 

(P-  n5)' 

Pia  Mater  Encephali. — The  pia  mater  forms  the  immediate 
investment  of  the  brain.  It  is  finer  and  more  delicate  than 
the  corresponding  membrane  of  the  spinal  cord,  and  it  follows 
closely  all  the  inequalities  on  the  surface  of  the  brain.  Thus, 
in  the  case  of  the  cerebrum,  it  dips  down  so  as  to  line  both 
sides  of  every  sulcus  and  form  a  fold  within  it.  On  the 
cerebellum  the  relation  is  not  so  intimate  ;  it  is  only  the 
larger  fissures  of  the  cerebellum  which  contain  folds  of  pia 
mater. 

The  larger  blood  vessels  of  the  brain,  as  we  have  noted, 
run  in  the  subarachnoid  space.  The  finer  twigs  enter  the 
pia  mater  and  ramify  in  it  before  proceeding  into  the  substance 
of  the  brain.  As  they  enter  they  carry  with  them  sheaths 
derived  from  the  pia  mater.  Consequently,  if  the  dissector 
raises  a  portion  of  this  membrane  from  the  surface  of  the 
cerebrum,  a  number  of  fine  processes  will  be  seen  to  be  with- 
drawn from  the  cerebral  substance.  These  are  the  blood- 
vessels, and  they  give  the  deep  surface  of  the  membrane  a 
rough  and  flocculent  appearance. 

The  pia  mater  is  not  confined  to  the  exterior  of  the  brain. 
A  fold  is  carried  into  its  interior.  This  will  be  exposed  in 
the  dissection  of  the  brain,  and  described  under  the  name  of 
the  velum  interpositum  or  the  tela  choroidea  superior. 

Dissection. — The  blood  vessels  of  the  brain  should  now  be  followed  out 
as  far  as  it  is  possible  to  do  so  without  laceration  of  the  brain  substance. 
Begin  by  stripping  the  arachnoidea  from  the  base  of  the  brain.  This  will 
bring  into  view  the  main  trunks.  In  describing  the  vessels  of  the  brain  it 
is  unfortunately  necessary  to  speak  of  many  parts  which  have  not  yet  come 
under  the  notice  of  the  dissector. 

Arteries  which  supply  Blood  to  the  Brain. — Four  main 
arterial  trunks  carry  blood  into  the  cranium  for  the  supply 
of  the  brain — viz.,  the  two  internal  carotid  arteries  and  the 
two  vertebral  arteries.  The  vertebral  arteries  enter  through 
the  foramen  magnum,  whilst  the  internal  carotid  arteries  gain 
admittance  through  the  carotid  canals.  These  vessels  have 
been  divided  in  the  removal  of  the  brain.  The  cut  end  of  the 
internal  carotid  will  be  seen  on  the  base  of  the  brain  immedi- 
ately to  the  outer  side  of  the  optic  nerve  ;  the  vertebral  lies 
on  the  side  of  the  medulla  oblongata.  A  very  remarkable  and 
complete  anastomosis  takes  place  on  the  base  of  the  brain  by 


MEMBRANES  AND   BLOOD  VESSELS  445 

the  inosculation  of  branches  which  spring  from  the  carotid  and 
vertebral  arterial  systems.  This  is  termed  the  circle  of  Willis. 
The  branches  which  take  part  in  this  anastomosis  are  placed 
in  that  large  expansion  of  the  subarachnoid  space  which  is 
termed  the  cisterna  basalis. 

Two  systems  of  branches,  both  going  to  the  cerebrum,  but 
differing  greatly  in  their  mode  of  distribution,  proceed  from 
the  vessels  forming  the  circle  of  Willis.  One  system  consists 
of  very  numerous  slender  twigs,  which,  as  a  rule,  come  off  in 
groups  in  certain  localities,  and  at  once  pierce  the  substance 
of  the  cerebrum  so  as  to  gain  its  interior.  These  are  the 
central  or  basal  branches.  The  other  system  is  composed  of 
branches  which  ramify  over  the  surface  of  the  cerebrum,  and 
are  termed  the  cortical  branches.  The  central  parts  of  the 
brain,  including  the  basal  ganglia,  receive  their  blood-supply 
from  the  basal  system,  and  the  vessels  which  constitute  this 
group  do  not  anastomose  with  each  other.  The  cortical 
vessels  supply  the  cerebral  cortex,  and  the  finer  branches 
which  ramify  in  the  pia  mater  anastomose  with  each  other. 
It  so  happens,  therefore,  that  neighbouring  vascular  districts  of 
the  cerebral  cortex  are  not  sharply  cut  off  from  each  other. 

Vertebral  Artery  (arteria  vertebralis).  —  The  vertebral 
artery  enters  the  subarachnoid  space  in  the  upper  part  of  the 
vertebral  canal  by  piercing  the  dura  mater  and  the  arachnoid 
mater.  Gaining  the  interior  of  the  cranium  through  the 
foramen  magnum,  it  is  continued  upwards  on  the  side  of  the 
medulla  oblongata.  Soon  it  inclines  forwards  towards  the 
front  of  the  medulla,  and,  meeting  its  fellow  of  the  opposite 
side  in  the  mesial  plane,  it  unites  with  it  at  the  lower  border 
of  the  pons  Varolii  to  form  the  basilar  artery. 

During  this  part  of  its  course  the  vertebral  artery  gives  off 
the  following  branches  : — 


i.    Posterior  meningeal. 

2.    Posterior  spinal. 

].    Posterior  inferior  cerebellar. 


4.  Anterior  spinal. 

5.  Bulbar. 


The  posterior  meningeal  bra?ich  (ramus  meningeus)  springs 
from  the  vertebral  artery  before  it  pi erces  the  dura  mater,  and 
is  distributed  in  the  posterior  cranial  fossa. 

The  posterior  spinal  (arteria  spinalis  posterior)  is  the  first 
branch  that  is  given  off  after  the  vertebral  artery  pierces  the 
dura  mater.  It  passes  downwards  on  the  spinal  cord  in  front 
of  the  posterior  nerve-roots  (p.   170). 


446 


THE  BRAIN 


The  posterior  inferior  cerebellar  (arteria  cerebelli  inferior 
posterior)  is  the  largest  branch  of  the  vertebral  artery,  and  it 
takes  origin  immediately  above  the  posterior  spinal  artery. 
It  pursues  a  tortuous  course  backwards  on  the  side  of  the 
upper  part  of  the  medulla,  between  the  nerve-roots  of  the 
hypoglossal,  and  then  between  the  roots  of  the  vagus.     Finally, 


Infundibulum 


Sixth  nerve 


Auditory  and 
facial  nerves 


Glosso-pharyn- 
geal  nerve 


Optic  nerve 

Internal  carotid 
artery 


Posterior 
communicating 

Third  nerve 

2^! — Posterior  cerebral 
^\       Superior 


cerebellar 
Tentorium 


Vagus  nerve 


Hypoglossal 

nerve 

Spinal  accessory 

nerve 

Section  through  Vt& 
the  medulla 


Basilar 
artery 

^Jj  |  Vertebral 
artery 

Superior  petrosal 
sinus 


Lateral  sinus 


Lateral  sinus 


Superior  longitudinal  sinus 


Occipital  sinus 


Straight  sinus  divided 

Fig.  t66. — Floor  of  the  Cranium  after  the  removal  of  the  Brain  and  the 
Tentorium  Cerebelli.  The  blood  vessels  forming  the  circle  of  Willis 
have  been  left  in  place. 

turning  round  the  restiform  body,  it  gains  the  vallecula  of  the 
cerebellum,  where  it  ends  by  dividing  into  two  terminal 
branches.  Of  these,  one  turns  backwards  in  the  sulcus, 
between  the  inferior  vermiform  process  and  the  lateral  hemi- 
sphere of  the  cerebellum,  whilst  the  other  ramifies  on  the 
posterior  part  of  the  inferior  surface  of  the  corresponding 
cerebellar  hemisphere. 

The  anterior  spinal  artery  (arteria  spinalis  anterior)  arises 


MEMBRANES  AND  BLOOD  VESSELS  447 

near  the  lower  border  of  the  pons  Varolii.  It  is  rare  to  find 
the  vessels  of  the  two  sides  of  equal  size.  They  converge 
on  the  anterior  surface  of  the  medulla,  and  unite  to  form  the 
commencement  of  the  median  vessel  which  extends  down- 
wards on  the  ventral  face  of  the  cord. 

The  bulbar  arteries  are  minute  vessels  which  enter  the 
substance  of  the  medulla,  and  spring  both  from  the  vertebral 
artery  itself  and  also  from  its  branches. 

Basilar  Artery  (arteria  basilaris). — The  basilar  artery,  which 
is  formed  by  the  union  of  the  two  vertebral  arteries,  is  a  short 
trunk  which  extends  in  the  mesial  plane  from  the  lower  to 
the  upper  border  of  the  pons  Varolii.  At  the  latter  point  it 
ends  by  dividing  into  the  two  posterior  cerebral  arteries.  The 
basilar  artery  lies  in  the  middle  part  of  the  cisterna  pontis, 
and  occupies  the  median  groove  on  the  ventral  or  anterior 
surface  of  the  pons  Varolii.  In  front  it  is  supported  by  the 
basilar  process  of  the  occipital  bone  and  the  dorsum  sellae  of 
the  sphenoid. 

The  branches  which  spring  from  the  basilar  artery,  for  the 
most  part,  proceed  outwards  from  either  side  of  the  vessel. 
They  are : — 


1.  Transverse. 

2.  Internal  auditory. 

3.  Anterior  inferior  cerebellar. 


4.  Superior  cerebellar. 

5.  Posterior  cerebral. 


The  transverse  arteries  (rami  ad  pontem)  are  numerous 
slender  twigs  which  run  outwards  on  the  surface  of  the  pons 
and  enter  its  substance.  The  auditory  artery  (arteria  auditiva 
interna)  will  be  seen  amongst  these.  It  follows  the  auditory 
nerve  into  the  internal  auditory  meatus,  and  is  distributed  to 
the  internal  ear. 

The  a?iterior  inferior  cerebellar  (arteria  cerebelli  inferior 
anterior)  inclines  outwards  and  backwards  to  reach  the  anterior 
part  of  the  inferior  surface  of  the  cerebellum. 

The  superior  cerebellar  artery  (arteria  cerebelli  superior)  is 
a  large  vessel  which  springs  from  the  basilar  close  to  its 
termination.  It  winds  outwards  and  backwards  along  the 
upper  border  of  the  pons  Varolii  to  reach  the  upper  surface 
of  the  cerebellum,  upon  which  it  spreads  out  in  a  number  of 
large   branches   which,    for   the    most   part,  take  a   backward 

course. 

Posterior  Cerebral  Artery  (arteria  cerebri  posterior). — 
Immediately  beyond  the  origin  of  the  two  superior  cerebellar 


44§ 


THE   BRAIN 


arteries,  the  basilar  trunk  bifurcates  into  the  two  posterior 
cerebral  arteries.  These  diverge  from  each  other,  and,  curv- 
ing outwards,  they  encircle  the  mesencephalon,  and  are  carried 
backwards  towards  the  under  surface  of  the  splenium  of  the 
corpus  callosum.  In  this  course  the  posterior  cerebral  artery 
lies  deeply  in  the  interval  between  the  corresponding  crus 
cerebri  and  the  hippocampal  gyrus,  and,  finally  passing  on  to 
the  tentorial  surface  of  the  cerebral  hemisphere,  it  disappears 
from  view  by  sinking  into  the  anterior  extremity  of  the  cal- 
carine  fissure.      In  this  fissure  the  artery  ends  by  dividing  into 


Paracentral  branch 


Precuneal  branch 


Marginal  branch 


Parieto- 
occipital 
branch 


Internal 
frontal 
jran?hes 


sM^'     Internal  orbit- 
al branches 
Anterior  cerebral  artery 


Calcarine  branch  \f  Posterior  cerebral  artery 

Temporal  branches 

Fig.  167. — Internal  and  Tentorial  Surfaces  of  the  left  Cerebral  Hemisphere. 
The  district  supplied  by  the  anterior  cerebral  artery  is  tinted  purple  ;  by 
the  middle  cerebral  artery,  blue  ;  and  by  the  posterior  cerebral  artery, 
red.      (Semi-diagrammatic.  1 


two  terminal  branches,   viz.,   the  calcarine   and   the   parieto- 
occipital (Figs.  167  and  168). 

The  third  or  oculo-motor  nerve  passes  forwards  in  the 
interval  between  the  posterior  cerebral  and  the  superior 
cerebellar  arteries,  close  to  the  place  where  they  arise  from 
the  basilar ;  and  the  small  fourth  or  trochlear  nerve  is  related 
to  the  posterior  cerebral  artery  as  it  winds  round  the  crus 
cerebri. 

The  following  branches  spring  from  the  posterior  cerebral  artery  : — 


Central  or  basal 


(  Postero-mesial. 
-  Postero-lateral. 
[Posterior  choroidal. 


[  Temporal. 
Cortical     -,  Calcarine. 


I  Parieto-occipital. 


MEMBRANES  AND  BLOOD  VESSELS         449 

The  postero- mesial  central  arteries  arise  close  to  the  origin  of  the  parent 
trunk.  They  proceed  upwards  in  the  interval  between  the  crura  cerebri, 
and,  piercing  the  locus  perforatus  posticus,  they  supply  the  optic  thalamus 
and  the  inner  part  of  the  crus  cerebri. 

The  postero -lateral  central  aiieries  are  a  group  of  small  slender  twigs 
which  arise  on  the  outer  surface  of  the  crus  cerebri,  and  go  to  the  corpora 
quadrigemina  and  the  optic  thalamus. 

The  posterior  choroidal  artery,  somewhat  larger,  goes  to  the  velum 
interpositum  and  the  choroid  plexus  of  the  lateral  ventricle  (Figs.  167 
and  168). 

The  temporal  branches,  two  or  three  in  number,  turn  outwards  over  the 
hippocampal  gyrus,  and  ramify  on  the  under  surface  of  the  temporal  lobe 
of  the  cerebrum  (Figs.  167  and  168). 

The  calcarine  branch  (arteria  occipitalis)  follows  the  calcarine  fissure  to 
the  occipital  pole  of  the  cerebral  hemisphere,  round  which  it  turns  to  reach 
the  outer  surface  of  the  occipital  lobe.  It  is  the  chief  artery  of  supply  to  the 
cuneus  and  the  lingual  convolution,  and  is  therefore  specially  concerned  in 
the  nutrition  of  the  visual  centres  in  the  cerebral  cortex  (Figs.  167  and  168). 

The  parietooccipital  artery  is  the  smaller  of  the  two  terminal  branches 
of  the  posterior  cerebral.  It  runs  upwards  in  the  parieto-occipital  fissure, 
and,  reaching  the  upper  margin  of  the  cerebrum,  it  turns  round  this  to 
reach  the  outer  surface  of  the  occipital  lobe.  It  supplies  branches  to  the 
cuneus  and  precuneus  (Fig.  167). 

Internal  Carotid  Artery  (arteria  carotis  interna). — The 
terminal  part  of  this  great  vessel  lies  on  the  outer  side  of  the 
optic  chiasma,  in  the  angle  between  the  optic  nerve  and  the 
optic  tract.  At  the  anterior  perforated  spot,  close  to  the 
commencement  of  the  Sylvian  fissure,  it  ends  by  dividing  into 
the  anterior  and  middle  cerebral  arteries  (Fig.  168).  The 
middle  cerebral  artery  is  the  larger  of  the  two  terminal  branches, 
and,  as  it  enters  the  Sylvian  fissure,  it  appears  to  be  the  con- 
tinuation of  the  parent  trunk.  The  anterior  cerebral  artery, 
on  the  other  hand,  proceeds  inwards  from  the  internal  carotid 
at  almost  a  right  angle.  This  explains  how  it  is  that  emboli 
pass  more  frequently  into  the  middle  cerebral  than  into  the 
anterior  cerebral  artery.  From  the  internal  carotid  artery, 
after  it  has  emerged  from  the  cavernous  sinus  (p.  328),  the 
following  branches  arise  : — 


1.  Ophthalmic  (already  studied, 

P-  339)- 

2.  Posterior  communicating. 


3.  Anterior  choroidal. 

4.  Middle  ceiebral. 

5.  Anterior  cerebral. 


The  posterior  communicating  artery  (arteria  communicans 
posterior)  is  as  a  rule  a  slender  branch  which  proceeds  back- 
wards to  join  the  posterior  cerebral  between  its  postero-mesial 
and  postero-lateral  groups  of  basal  twigs  (Figs.  168  and  170). 

The  atitcrior  choroidal  artery  (arteria  choroidca)  enters  the 

vol.  11—29 


45° 


THE  BRAIN 


descending  cornu  of  the  lateral  ventricle,  and  passes  into  the 
choroid  plexus  in  that  cavity  (Fig.  168). 

Anterior  Cerebral  Artery  (arteria  cerebri  anterior). — The 
anterior  cerebral  in  the  first  instance  takes  a  horizontal  course 
inwards  and  forwards  (Fig.  168).  It  passes  above  the  optic 
chiasma   and   immediately  in    front    of   the    lamina    cinerea, 


Internal  orbital  branches 


Anterior  cerebral  artery 

Anterior  communicating 

Internal  carotid  artery __    /J^V^"^ 
Middle  cerebral  artery  -^ 

Posterior  communicatin 


Superior  cerebellar  artery^ 

Basilar  artery'' 

Posterior  choroidal  artery 

Posterior  cerebral  artery 
Calcarine  fissure 


Olfactory  sulcus 


External  orbital  branches 


Anterior  choroidal 
artery 


Temporal 
branches 


Occipitotemporal 
sulcus 


ollateral  fissure 


Fig.  168. — Inferior  Surface  of  the  Cerebral  Hemisphere.  The  districts  sup- 
plied by  the  three  cerebral  arteries  are  tinted  differently  :  posterior  cerebral 
artery,  red;   middle  cerebral  artery,  blue  ;  anterior  cerebral  artery,  purple. 

and  finally  reaches  the  hinder  end  of  that  part  of  the  great 
longitudinal  fissure  which  separates  the  frontal  lobes  of  the 
cerebrum.  Here  it  lies  close  to  its  fellow  of  the  opposite 
side,  and  the  two  vessels  are  connected  by  a  short  transverse 
trunk  of  communication,  termed  the  a?iterior  communicating 
artery  (arteria  communicans  anterior).  The  anterior  cerebral 
artery  now  enters  the  great  longitudinal  fissure,  and  is  carried 
forwards  and  upwards  on  the  inner  surface  of  the  frontal  lobe 
towards  the  genu  or  anterior  extremity  of  the  corpus  callosum 


MEMBRANES  AND  BLOOD  VESSELS 


45i 


(Fig.  167).  Round  this  it  turns,  and  it  is  then  continued 
backwards  on  the  upper  surface  of  the  corpus  callosum. 
Very  much  reduced  in  size,  it  gives  off  its  terminal  branch 
(termed  the  artery  of  the  corpus  callosum),  which  may  be 
traced  as  far  as  the  splenium  or  posterior  end  of  the  corpus 
callosum. 

Numerous  branches  proceed  from  the  anterior  cerebral  artery  : — 
Basal  or  central  {  Antero-mesial. 


fin 
J  Ar 

I  Middle  internal  frontal  (or  paracentral). 


ferior  internal  frontal  (or  internal  orbital). 
Anterior  internal  frontal. 


Cortical 

Posterior  internal  frontal  (or  precuneal). 
The  antero-mesial  group  of  arteries  pierce  the  base  of  the  brain  in  front 


Ascending  parietal  artery       Fissure  of  Rolando 


Ascending  frontal  artery 


Parieto-temporal  artery 


Inferior 


Middle 
frontal 
sulcus 


External 
parieto- 
occipital 
fissure 


Inferior  frontal  artery 

Posterior  limb  of  fissure  of  Sylvius 

Temporal  branches 

FlG.  169. — Outer  Surface  of  the  Cerebral  Hemisphere.  The  districts  supplied 
by  the^ three  cerebral  arteries  are  tinted  differently:  anterior  cerebral, 
purple;  middle  cerebral,  blue  ;  posterior  cerebral,  red.  (Semi-diagram- 
matic. 1 


of  the  optic  chiasm  a.     They  supply  the  rostrum  of  the  corpus  callosum, 
the  lamina  cinerea,  and  the  septum  lucidum. 

The  inferior  internal  frontal  branches  (internal  orbital)  are  two  or 
three  in  number,  and  turn  round  the  margin  of  the  great  longitudinal 
fissure  to  reach  the  inner  part  of  the  orbital  surface  of  the  frontal  lobe. 
They  supply  the  gyrus  rectus,  the  olfactory  peduncle  and  bulb,  and  the 
internal  orbital  convolution  (ligs.   167  and  168). 

The  anterior  internal  frontal  artery  ramifies  upon  the  fore-part  of  the 
inner  surface  of  the  frontal  lobe,  and  its  terminal  twigs  turn  round  the 
upper  margin  of  the  cerebral  hemisphere,  and  supply  the  outer  surface  of 
tin-  frontal  lobe  as  far  down  as  the  sulcus  frontalis  medius  (Fig.  169). 

The  middle  internal  frontal  artery  (paracentral)  ramifies  on  the  inner 


452  THE  BRAIN 

surface  of  the  frontal  lobe  behind  the  preceding  branch.  Its  terminal  part 
passes  over  the  paracentral  convolution,  and  reaches  the  adjacent  portion 
of  the  outer  surface  of  the  cerebral  hemisphere  (Fig.  169). 

The  posterior  internal  frontal  artery  (precuneal)  ramifies  on  the  inner 
surface  of  the  precuneus,  and  its  terminal  twigs  turn  round  the  upper 
margin  of  the  cerebral  hemisphere  to  gain  its  outer  surface. 

Middle  Cerebral  Artery  (arteria  cerebri  media). — The 
middle  cerebral  artery  passes  outwards  and  upwards  in  the 
Sylvian  fissure,  and  soon  breaks  up  into  a  number  of  large 
terminal  branches,  which  spread  out  on  the  surface  of  the 
island  of  Reil.  Before  the  posterior  limb  of  the  Sylvian 
fissure  is  opened  up  so  as  to  expose  the  island  of  Reil,  these 
branches  are  observed  streaming  out  from  between  its  two 
lips  (Fig.  169).  They  then  diverge  so  as  to  supply  a  wide 
area  of  cortex  on  the  outer  surface  of  the  cerebral  hemisphere. 

The  branches  which  spring  from  the  middle  cerebral  artery  may  be 
classified  thus  : — 

» 

Central  or  basal       1    .  1/1 

branches.  /  Anterolateral. 


Cortical  branches.    < 


(  External  orbital. 
Frontal         -!    External  inferior  frontal. 
(^  Ascending  frontal. 

Parietal         {  Ascending  parietal. 

Parieto-temporal. 
Temporal. 

The  ant ero -lateral  group  of  basal  arteries  are  very  numerous.  They 
pierce  the  anterior  perforated  spot  and  supply  the  lenticular  nucleus,  the 
internal  and  the  external  capsule,  the  caudate  nucleus,  and  a  portion  of  the 
optic  thalamus. 

The  frontal  and  parietal  branches  turn  round  the  upper  lip  of  the 
posterior  limb  of  the  Sylvian  fissure  and  ascend  on  the  outer  surface  of  the 
cerebrum.  The  frontal  branches  are  :  (1)  an  external  orbital  to  the  outer 
part  of  the  orbital  surface  of  the  frontal  lobe  ;  (2)  an  inferior  external 
frontal  to  the  inferior  frontal  convolution  ;  (3)  an  ascending  frontal  which 
runs  upwards  in  relation  to  the  ascending  frontal  convolution. 

The  ascending  parietal  branch  extends  in  an  upward  and  backward 
direction  in  relation  to  the  ascending  parietal  convolution,  and  its  ter- 
minal twigs  supply  the  greater  part  of  the  cortex  of  the  superior  parietal 
convolution. 

The  pai'ieto-temporal  branch  is  a  very  large  artery  which  issues  from  the 
hinder  part  of  the  posterior  limb  of  the  fissure  of  Sylvius  and  sends  branches 
upwards  to  the  inferior  parietal  convolution,  and  others  which  incline  down- 
wards over  the  hinder  part  of  the  temporal  lobe.  Its  twigs,  as  a  rule,  do 
not  encroach  upon  the  outer  surface  of  the  occipital  lobe. 

The  temporal  branches,  two  or  three  in  number,  issue  from  the  posterior 
limb  of  the  Sylvian  fissure,  and  turning  downwards  and  backwards  over 
its  lower  lip  {i.e.,  the  first  temporal  convolution),  they  ramify  upon  the 
outer  surface  of  the  temporal  lobe. 


MEMBRANES  AND   BLOOD  VESSELS 


453 


Circle  of  Willis  (circulus  arteriosus  Willisii). — This  re- 
markable anastomosis  is  placed  on  the  base  of  the  brain  in 
the  deep  hollow  in  front  of  the  pons  Varolii.  It  takes  the 
form  of  a  heptagonal  or  hexagonal  ring,  and  the  vessels  which 
compose  it  lie  in  the  large  basal  subarachnoid  space.  In 
front  it  is  closed  by  the  anterior  communicating  artery  which 
links  together  the  two  anterior  cerebral  arteries.  On  either 
side   is   the   posterior   communicating   artery  connecting  the 


Anterior  cerebral  artery 

Anterior  communicating 
Internal,  carotid 

Middle  cerebral 


Antero-lateral  basal  arteries 
Posterior  communicating 


Postero-mesial  basal  arterie> 
*"  '"'^— ^  -.   p"-r *•"*•■'"-  cerebral  artery 


V 


"Superior  cerebellar  artery 


Fig.   170. — Diagram  of  the  Circle  of  Willis. 

internal  carotid  (from  which  the  anterior  cerebral  springs; 
with  the  posterior  cerebral.  Behind,  the  arterial  ring  is  com- 
pleted by  the  bifurcation  of  the  basilar  artery  into  the  two 
posterior  cerebral  vessels  (Fig.  170).  As  a  rule  the  circle 
of  Willis  is  not  symmetrical.  The  right  posterior  communi- 
cating artery  is  almost  invariably  larger  than  its  fellow  of  the 
opposite  side. 

Dissection.     The    brain    being   placed    with    its  base    uppermost,    the 

tor  should  proceed  to  remove  the  blood  vessels  and  membranes  from 

its  surface.      This  must   be  done   with  th  and   a  pair  of  sci 

It  is  a  dissection  whirl,  requires  very  delicate  manipulation,  because  the 

cranial  nerves  at  their  points  of  attachment  to  the  brain  are  so  intimately 

u— 29  a 


454  THE  BRAIN 

connected  with  the  pia  mater  that  any  undue  traction  applied  to  the 
membranes  will  tear  the  nerves  away.  Indeed,  in  the  case  of  the 
medulla  oblongata,  the  dissector  is  advised  to  leave  the  pia  mater  in 
position  until  the  nerve  roots  have  been  studied.  The  relation  of  the  pia 
mater  to  the  fourth  ventricle  likewise  renders  this  desirable.  In  so  far  as 
the  other  nerves  are  concerned,  the  pia  mater  may  be  divided  carefully 
around  their  roots  with  the  scissors. 

In  removing  the  arachnoidea  and  pia  mater  from  the  outer  surface  of 
the  cerebrum,  it  is  well  to  raise  it  in  the  first  instance  from  the  margins  of 
the  hemisphere,  and  then  work  towards  the  fissure  of  Sylvius.  By  so 
doing,  the  membranes  and  vessels  within  this  great  fissure  and  in  relation 
to  the  island  of  Reil  can  be  withdrawn  without  damage  to  the  brain 
substance.  Of  course,  at  the  present  stage,  the  membranes  cannot  be 
removed  from  every  part  of  the  brain  ;  but  as  the  dissection  proceeds, 
opportunities  for  completing  the  process  will  arise. 


BASE  OF  BRAIN. 

Interpeduncular  Space. — When  the  membranes  are  re- 
moved from  the  base  of  the  brain,  the  crura  cerebri,  two  large 
rope-like  strands,  will  be  seen  issuing  from  the  upper  aspect  of 
the  pons  Varolii.  Placed  close  together  as  they  emerge  from 
the  pons,  they  diverge  as  they  proceed  upwards  and  for- 
wards, and  finally  each  eras  disappears  into  the  corresponding 
side  of  the  cerebrum.  Turning  round  the  outer  aspect  of 
each  crus  where  it  passes  into  the  cerebrum  will  be  seen  a 
flattened  band,  called  the  optic  tract.  These  bands  converge 
as  they  pass  forwards,  and  are  finally  joined  together  by  a 
short  transverse  commissural  portion,  termed  the  optic  chiasma. 
This  chiasma  is  placed  below  the  hinder  end  of  that  portion 
of  the  great  longitudinal  fissure  which  intervenes  between  the 
frontal  lobes  of  the  cerebrum.  The  optic  nerve  is  continued 
forwards  and  outwards  from  the  chiasma  and  the  tract. 

The  crura  cerebri,  the  optic  tracts,  and  the  optic  chiasma 
enclose  a  deep  rhomboidal  or  lozenge-shaped  interval  on  the 
base  of  the  brain,  which  is  termed  the  i?iterpeduncular  space. 
Within  the  limits  of  this  area  the  following  parts  may  be 
seen  as  we  pass  from  behind  forwards: — (i)  the  locus  per- 
foratus  posticus;  (2)  the  corpora  mammillaria ;  (3)  the  tuber 
cinereum,  attached  to  which  is  the  infundibulum  of  the 
pituitary  body.  These  structures  form  the  floor  of  the  third 
ventricle  of  the  brain. 


BASE  OF  BRAIN 


455 


The  oculo-motor  nerves  issue  from  the  brain  within  the 
interpeduncular  space.  Each  nerve  emerges  from  the  inner 
side  of  the  corresponding  crus  cerebri. 

Locus   Perforatus   Posticus. — At   its   posterior  angle,   im- 


Optic  chiasma 


Infundibulum 


Corpora 
mammillari 


Locus 

perforatus 
posticus 


Olfactory  bulb 


Sixth 
nerve 


_  lossal 
nerve 


Pyramid 
Spinal  cord  (cut) 


•Olfactory  tract 


Optic  nerve 


Locus  perfor- 
atus anticus 

Optic  tract 


Tuber 
cinereum 

Third  nerve 


Fourth  nerve 
Fifth  nerve 


Facial  nerve 
Auditory  nerve 

Pars  intermedia 

NGlosso-pharyngeal 
nerve 

\ 
Vagus  nerve 

Spinal  accessory  nerve 


Hypoglossal  nerve 
FlG.   171.    -'Ill'-  Hi-,'-  of  tin.'  Brain  with  the  Cranial  Xerves  attached. 


mediately  in  front  of  the  pons  Varolii,  the  interpeduncular 
space  is  very  deep,  and  is  floored  by  a  layer  of  grey  matter 
which  is  perforated  by  numerous  small  apertures.  This  is 
the  locus  perforatus  posticus.  From  the  apertures  which  are 
11— 29  b 


456  THE  BRAIN 

dotted  over  its  surface  the  postero-mesial  basal  branches   of 
the  posterior  cerebral  artery  have  been  withdrawn. 

Corpora  Mammillaria. — These  are  two  small  white  pea- 
like  eminences  placed  side  by  side  in  front  of  the  locus 
perforatus  posticus.  At  a  later  stage  of  the  dissection  their 
connexion  with  the  anterior  pillars  of  the  fornix  will  be 
brought  out. 

Tuber  Cinereum. — This  is  a  slightly  raised  field  of  grey 
matter  which  occupies  the  interval  between  the  anterior 
portions  of  the  optic  tracts  in  front  of  the  corpora  mammillaria. 
Springing  from  the  fore-part  of  the  tuber  cinereum,  immedi- 
ately behind  the  optic  chiasma,  is  the  infundibulum  or  stalk 
of  the  pituitary  body.  In  the  removal  of  the  brain  its  con- 
nexion with  that  body  has  been  severed. 

Locus  Perforatus  Anticus. — This  is  a  small  triangular 
district  of  grey  matter  on  each  side,  which  is  bounded  behind 
by  the  uncinate  extremity  of  the  hippocampal  gyrus,  in  front 
by  the  diverging  roots  of  the  olfactory  peduncle,  and  internally 
by  the  optic  tract.  It  leads  in  an  outward  direction  into  the 
Sylvian  fissure,  and  is  perforated  by  the  antero-lateral  groups 
of  basal  arteries.  The  grey  matter  in  this  area  is  continuous 
above  with  the  grey  matter  of  the  lenticular  nucleus. 

Lamina  Cinerea. — If  the  optic  chiasma  be  now  gently 
raised  with  the  forceps,  a  thin  lamina  will  be  noticed  passing 
upwards  from  it  into  the  great  longitudinal  fissure,  to  become 
connected  with  the  rostrum  of  the  corpus  callosum.  This  is 
the  la?nina  cinerea.  It  closes  the  third  ventricle  in  front,  and 
is  continuous  on  either  side  with  the  grey  matter  of  the  locus 
perforatus  anticus. 

Superficial  Origins  of  the  Cranial  Nerves. — Twelve  cranial 
nerves  are  enumerated  as  arising  from  the  brain  on  either 
side  of  the  mesial  plane.  These  are  the  olfactory,  or  first ; 
the  optic,  or  second ;  the  oculo-motor,  or  third ;  the  troch- 
lear, or  fourth ;  the  trigeminal,  or  fifth  ;  the  abducent,  or 
sixth ;  the  facial,  or  seventh  ;  the  auditory,  or  eighth ;  the 
glossopharyngeal,  or  ninth ;  the  vagus,  or  tenth  ;  the  spinal 
accessory,  or  eleventh  ;  and  the  hypoglossal,  or  twelfth. 

Each  of  these  nerves  is  said  to  have  a  "  superficial "  and  a 
"deep  "  origin.  By  the  term  "superficial  origin  "  we  refer  to 
the  point  where  its  fibres  enter  or  leave  the  brain  surface ;  by 
the  term  "  deep  origin  "  we  indicate  the  connexions  which 
are   established   by   the   fibres   of   the   different   nerves   with 


BASE  OF  BRAIN 


457 


nuclei  or  clusters  of  nerve -cells  within  the  substance  of  the 
brain.  These  nuclei  are  of  two  kinds:  (i)  those  in  con- 
nexion with  which  the  afferent  or  entering  nerves  end ;  and 
(2)  those  from  which  the  efferent  or  emerging  nerves  arise. 
It  is  the  superficial  attachments  only  which  come  under  our 
notice  at  the  present  time. 

No  fewer  than  eight  of  the  cranial  nerves  have  a  superficial 
attachment  to  the  medulla  oblongata  and  the  pons  Varolii. 


^=* 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum 

externum 

Corpus  geniculatum 

internum 

Locus  perforatus 

posticus 


Middle  peduncle 
of  cerebellum 


Restiform  body 

Olive 

Pyramid 

Anterior  superficial 

arcuate  fibres 

Decussation  of 
pyramids 


Optic  nerve 
Infundibulum 
Tuber  cinereum 

Corpus  mammillare 

Oculo-motor  nerve 

(in.) 
*?    Trochlear  nerve  (iv.) 
-—   winding  round  crus 

cerebri 


Trigeminal  nerve  (v.) 
Abducent  nerve  (vi.) 
Facial  nerve  (vil.) 
Auditory  nerve  (vin.) 

Vago-glosso-pharyn- 
geal  nerve  (ix.  and  x.) 

Fascicles  of  hypo- 
glossal nerve  (xn.) 

cut  short 

Spinal  accessory 
nerve  (xi.) 

First  cervical  nerve 


Fig.   172. — Front  view  of  the  Medulla,  Pons,  and  Mesencephalon 
of  a  full-time  Foetus. 


Hypoglossal  Nerve.  —  Upon  the  lateral  aspect  of  the 
medulla,  in  its  upper  half,  a  very  conspicuous  oval  prominence 
called  the  olivary  eminence  may  be  distinguished.  A  distinct 
sulcus  or  groove,  which  passes  downwards  in  front  of  this 
body,  separates  it  from  an  elongated  strand,  termed  the 
pyramid  of  the  medulla.  From  the  bottom  of  this  sulcus  a 
continuous  series  of  nerve  fascicles  will  be  seen  to  issue  along 
the  whole  length  of  the  medulla.  These  nerve  fascicles 
belong  to  two  different  nerves.     Those  which  issue  from  the 


458  THE   BRAIN 

lower  part  of  the  groove,  below  the  level  of  the  olivary 
eminence,  belong  to  the  anterior  root  of  the  first  cervical 
nerve  ;  those  which  emerge  from  the  upper  part  of  the  groove, 
in  the  interval  between  the  olivary  body  and  the  pyramid, 
form  the  hypoglossal  nerve. 

Glossopharyngeal,  Vagus,  and  Spinal  Accessory  Nerves. — 
Behind  the  olivary  eminence,  between  it  and  a  prominence 
called  the  restiform  body,  there  is  another  continuous  row  of 
nerve  fascicles  connected  with  the  medulla.  These  extend 
downwards  beyond  the  level  of  the  olivary  eminence,  and  are 
attached  to  the  whole  length  of  the  medulla  in  linear  order. 
They  belong  to  three  nerves,  but  it  is  impossible  at  present 
(seeing  that  the  nerve-trunks  that  they  build  up  are  divided) 
to  determine  precisely  the  number  of  roots  which  belong  to 
each.  From  below  upwards  the  nerves  which  they  form  are 
the  spinal  accessory,  the  vagus,  and  the  glosso-pharyngeal.  The 
vagus  and  the  glosso-pharyngeal,  which  issue  from  the  interval 
between  the  olivary  eminence  and  the  restiform  body,  have 
their  fascicles  of  origin  much  more  closely  crowded  together 
than  the  spinal  accessory. 

The  medullary  roots  of  the  spinal  accessory  constitute 
only  one  part  of  that  nerve.  The  spinal  part  springs  from 
the  spinal  cord,  as  low  down  as  the  sixth  cervical  nerve,  by  a 
series  of  roots  which  issue  from  the  lateral  column  behind  the 
attachment  of  the  ligamentum  denticulatum. 

Auditory  and  Facial  Nerves. — These  issue  close  together 
at  the  lower  border  of  the  pons  Varolii,  and  immediately 
above  the  restiform  body.  The  auditory  nerve  is  the  larger 
of  the  two,  and  lies  on  the  outer  side  of  the  facial.  Its  two 
roots,  termed  respectively  the  cochlear  and  the  vestibular, 
embrace  the  restiform  body. 

The  facial  nerve  issues  from  the  pons  close  to  its  lower 
border,  and  immediately  to  the  inner  side  of  the  auditory 
nerve.  Between  these  two  nerves  a  slender  filament  will  be 
observed.  This  is  the  pars  intermedia  of  Wrisberg.  It  joins 
the  facial  in  the  internal  auditory  meatus. 

Abducent  Nerve. — This  is  a  small  nerve,  which  emerges 
from  the  front  of  the  medulla  in  the  groove  between  the  lower 
border  of  the  pons  Varolii  and  the  outer  part  of  the  anterior 
pyramid. 

Trigeminal  or  Fifth  Nerve. — This  is  the  largest  of  all  the 
cranial  nerves.     It  appears  on  the  side  of  the  pons  Varolii, 


BASE  OF  BRAIN 


459 


nearer  its  upper  than  its  lower  border,  and  in  a  line  with  the 
facial  and  auditory  nerves.  It  consists  of  two  roots — a  large 
sensory  root  composed  of  a  great  number  of  fasciculi  loosely 
held  together,  and  a  small  more  compact  motor  root  which 
emerges  in  front  and  slightly  to  the  inner  side  of  the  point  at 
which  the  sensory  root  enters  the  pons. 

Trochlear  Nerve. — The  superficial  origin  of  the  trochlear 
or  fourth  nerve  cannot  be  seen  at  present.     It  emerges  from 


Oculo-motor  nerve 


Trochlear  nerve 

Sensory  root  of  the  trigeminal  nerve 
Motor  root  of  the  trigeminal 
nerve 

\bducent  nerve 

Facial  nerve 
NSKk       Cut  edge  of  the 


tentorium 


Pars  inter- 
media 
Auditory  nerve 

Right  lateral  sinus 

losso-pharyngeal 
nerve 

agus  nerve 
pinal  accessory  nerve 

Vertebral  artery 
Hypoglossal  nerve 
First  spinal  nerve 
accessory  nerve 

Fig.  173. — Section  through  the  Head  a  little  to  the  right  of  the  Mesial 
Plane.  It  shows  the  posterior  cranial  fossa  and  the  upper  part  of  spinal 
canal  after  the  removal  of  the  brain  and  the  cord. 

the  valve  of  Vieussens,  on  the  dorsal  aspect  of  the  brain-stem. 
It  is  a  delicate  little  nerve  which  has  a  long  intracranial 
course,  and  may  be  observed  winding  round  the  outer  side  of 
the  crus  cerebri,  between  the  cerebrum  and  cerebellum. 

Oculomotor  Nerve. — This  may  be  seen  within  the  inter- 
peduncular space.  It  issues  by  several  fascicles  from  the 
sulcus  oculomotorius  on  the  inner  face  of  the  crus  cerebri. 

Optic  Nerve. — This  is  a  large  round  nerve  which  proceeds 
outwards  and  forwards  from  the  optic  tract  and  optic  chiasma. 
The  origin  of  the  optic  tract  will  be  studied  at  a  later  stage. 


460 


THE  BRAIN 


Olfactory  Nerves. — These  arise  from  the  olfactory  bulb  or 
lobe,  and  enter  the  nasal  chamber  through  the  foramina  in 
the  cribriform  plate  of  the  ethmoid  bone. 

General  Connexions  of  the  Several  Parts  of  the  Brain. — 
Before  proceeding  to  the  more  particular  study  of  the  different 
parts  of  the  brain,  it  is  well  that  the  student  should  acquire 
a  general  conception  of  the  manner  in  which  these  are  con- 
nected with  each  other.  In  the  posterior  cranial  fossa,  below 
the  tentorium,  are  placed  the  medulla  oblongata,  the  pons 
Varolii,   and   the    cerebellum.      These   structures   surround  a 


A.  Cerebrum. 

B.  Cerebellum. 
D.   Medulla. 

C.  Pons  Varolii. 
b,  a.   Mesencephalon. 

c.  Middle  peduncle  of 
cerebellum. 

d.  Inferior  peduncle  ot 
cerebellum. 

e.  Sylvian  fissure. 

Fig.  174. — Diagrammatic  view  of  the  manner  in  which  the  several  parts  of 
the  Brain  are  connected  with  each  other.      ( From  Schwalbe. ) 

cavity  which  is  called  the  fourth  ventricle  of  the  brain,  and 
all  stand  in  intimate  connexion  with  each  other.  The 
medulla  oblongata  is  for  the  most  part  carried  upwards  into 
the  pons  Varolii,  but  at  the  same  time  two  large  strands  on 
its  posterior  or  dorsal  aspect,  termed  the  restiform  bodies, 
are  prolonged  into  the  cerebellum,  and  constitute  its  ififerior 
peduncles,  or  the  bonds  of  union  between  the  medulla  and  the 
cerebellum  (Fig.  174,  d).  The  transverse  fibres  of  the  pons 
Varolii  are  gathered  together  on  either  side  in  the  form  of  a 
large  rope-like  strand.  This  disappears  into  the  correspond- 
ing hemisphere  of  the  cerebellum,  and  constitutes  its  middle 
peduncle  (Fig.  174,  c). 


BASE  OF  BRAIN  461 

The  great  mass  of  the  brain  is  termed  the  cerebrum. 
This  occupies  the  anterior  and  middle  cranial  fossae,  and 
extends  backwards  into  the  occipital  region  above  the 
tentorium  and  the  cerebellum.  The  greater  part  of  the 
cerebrum  is  formed  by  the  cerebral  hemispheres,  which  are 
separated  from  each  other  in  the  mesial  plane  by  the  great 
longitudinal  fissure.  At  the  bottom  of  this  fissure  may  be 
seen  the  corpus  callosum,  a  broad  commissural  band  which 
connects  the  two  cerebral  hemispheres  with  each  other. 
Each  hemisphere  is  hollow — the  cavity  in  its  interior  being 
termed  the  lateral  ventricle  of  the  brain.  Between  and  below 
the  cerebral  hemispheres,  and  almost  completely  concealed 
by  them,  is  the  inter-brain  or  the  thala?nencephalon.  The 
principal  parts  forming  this  portion  of  the  brain  are  the  two 
optic  thalami,  between  which  is  the  third  ventricle  of  the  brain 
— a  deep,  narrow  cavity  occupying  the  mesial  plane.  The 
third  ventricle  communicates  with  the  lateral  ventricles  through 
twro  small  apertures,  termed  the  foramina  of  Monro. 

The  cerebrum  is  connected  with  the  parts  in  the  posterior 
cranial  cavity  (pons  Varolii,  cerebellum,  and  medulla  oblongata) 
by  a  narrow  stalk  called  the  i?iid-brain,  or  the  mesencephalon. 
The  mid-brain  is  built  up  of  the  crura  cerebri,  passing  from 
the  pons  Varolii  to  the  cerebrum  (Fig.  174,  a),  the  corpora 
quadrigemina  forming  its  dorsal  part  (Fig.  174,  b),  the  superior 
cerebellar  peduncles  proceeding  from  the  cerebellum  to  the 
cerebrum,  etc.  It  is  tunnelled  by  a  narrow  passage — the 
aqueduct  of  Sylvius — which  extends  between  the  fourth  and 
the  third  ventricles. 


THE  CEREBRUM. 

Cerebral  Hemispheres. — Each  cerebral  hemisphere  presents 
an  external,  an  internal,  and  an  inferior  surface,  separated  from 
each  other  by  more  or  less  distinctly  marked  borders.  The 
external  surface  is  convex,  and  is  adapted  to  the  concavity  of 
the  cranial  vault.  The  internal  surface  is  flat  and  perpen- 
dicular, and  is  more  or  less  completely  separated  from  the 
corresponding  surface  of  the  opposite  side  by  the  falx  cerebri, 
which  occupies  the  great  longitudinal  fissure.  The  inferior 
surface  is  irregular,  and  is  adapted  to  the  anterior  and  middle 
cranial  fossa:,  and  also  to  the  upper  surface  of  the  tentorium 


462  THE   BRAIN 

cerebelli.  Traversing  this  surface  in  a  transverse  direction, 
nearer  the  anterior  end  of  the  hemisphere  than  the  posterior 
end,  is  the  stem  of  the  Sylvian  fissure  (Fig.  171).  This  deep 
cleft  divides  the  inferior  surface  into  a  front  or  orbital  area, 
which  rests  upon  the  orbital  plate  of  the  frontal  bone,  and  is 
consequently  concave  from  side  to  side,  and  a  more  extensive 
posterior  or  tentorial  area,  which  lies  on  the  floor  of  the  lateral 
part  of  the  middle  cranial  fossa  and  the  upper  surface  of  the 
tentorium  cerebelli.  This  portion  of  the  inferior  surface  is 
arched  from  before  backwards,  and  looks  inwards  as  well  as 
downwards. 

The  borders  which  separate  these  surfaces  from  each 
other  are  the  supero-mesial,  the  superciliary,  the  infero-lateral, 
and  the  internal  occipital.  The  supero-7nesial  border,  convex 
from  before  backwards,  intervenes  between  the  internal  and 
external  surfaces.  The  superciliary  border  is  highly  arched, 
and  separates  the  orbital  surface  from  the  external  surface. 
-The  i?ifero-lateral  border  marks  off  the  tentorial  surface  from 
the  external  surface.  The  internal  occipital  border  is  not  very 
distinct,  except  in  cases  where  the  brain  has  been  hardened 
in  situ.  It  extends  from  the  posterior  extremity  of  the  hemi- 
sphere to  the  hinder  end  of  the  corpus  callosum,  and  inter- 
venes between  the  mesial  and  tentorial  surfaces. 

The  most  projecting  part  of  the  anterior  end  of  the 
cerebral  hemisphere  is  usually  called  the  frontal  pole,  whilst 
the  most  projecting  part  of  the  hinder  end  is  termed  the 
occipital  pole.  Again,  on  the  under  surface  of  the  hemisphere, 
the  prominent  point  of  cerebral  substance,  which  extends 
forwards  below  the  Sylvian  fissure,  receives  the  name  of  the 
temporal  pole.  In  a  well-hardened  brain  a  broad  groove  is 
usually  present  on  the  inner  aspect  of  the  occipital  pole  of  the 
right  hemisphere.  This  corresponds  to  the  commencement 
of  the  right  lateral  venous  sinus. 

Great  Longitudinal  Fissure  (incisura  pallii). — This  great 
mesial  cleft  is  occupied  by  the  fold  of  dura  mater  termed  the 
falx  cerebri.  In  front  and  behind,  it  completely  separates  the 
cerebral  hemispheres  from  each  other,  but  in  its  middle  part 
it  is  floored  by  the  corpus  callosum — the  commissural  band 
which  passes  between  the  hemispheres  and  connects  them 
together.  The  upper  surface  of  the  corpus  callosum  can  be 
displayed  by  gently  drawing  asunder  the  two  sides  of  the 
incisura  longitudinalis. 


THE  CEREBRUM  463 

Dissection. — If  two  brains  are  available,  the  dissector  is  advised  at  this 
stage  to  separate  in  one  of  these  the  cerebrum  from  the  cerebellum,  pons, 
and  medulla,  by  cutting  transversely  through  the  mid  brain.  The  cerebrum 
may  then  be  split  in  the  mesial  plane  by  placing  a  long  knife  in  the  longi- 
tudinal fissure,  and  dividing  with  one  sweep  the  various  parts  which  connect 
the  two  sides  to  each  other.  By  this  proceeding,  the  three  surfaces  of  each 
cerebral  hemisphere  are  exposed,  and  the  gyri  and  sulci  can  be  fully  and 
satisfactorily  studied.  If  only  one  brain  is  at  the  disposal  of  the  student,  he 
should  not  make  this  dissection,  but  endeavour  to  follow  out  the  gyri  and 
sulci  with  the  various  parts  of  the  brain  in  position.  No  doubt  he  studies 
the  hemisphere  in  this  way  at  a  disadvantage,  but  as  the  dissection  goes  on, 
opportunities  will  occur  which  will  enable  him  to  examine  those  districts 
of  the  surface  which  he  can  only  see  imperfectly  at  present. 

Cerebral  Gyri  and  Sulci. — The  surface  of  the  cerebral 
hemispheres  is  rendered  highly  irregular  by  the  presence  of 
convolutions  or  gyri,  separated  from  each  other  by  intervening 
furrows,  termed  sulci  or  fissures.  The  surface  pattern,  which 
is  presented  by  these  gyri  and  sulci,  is  in  its  general  features 
the  same  in  all  human  brains ;  but  when  the  comparison  is 
pushed  into  more  minute  detail,  many  differences  become 
manifest,  not  only  in  the  brains  of  different  individuals,  but 
also  in  the  two  cerebral  hemispheres  of  one  individual. 

Of  the  furrows  we  have  to  recognise  two  varieties,  viz., 
complete  and  incomplete.  The  complete  fissures  are  few  in 
number,  and  they  consist  of  inwardly  directed  folds  which 
involve  the  whole  thickness  of  the  cerebral  wall.  They  con- 
sequently show  in  the  interior  of  the  cerebral  cavity  or  lateral 
ventricle  in  the  form  of  internal  elevations  on  its  wall.  In 
this  category  we  include  (1)  the  dentate  or  hippocampal 
fissure  ;  (2)  the  anterior  portion  of  the  calcarine  fissure;  and 
(3)  a  portion  of  the  collateral  fissure.  The  incomplete  sulci  are 
merely  furrows  of  varying  depth  which  do  not  produce  any 
effect  on  the  inner  surface  of  the  ventricular  wall. 

General  Structure  of  the  Cerebral  Hemispheres. — Each 
cerebral  hemisphere  is  composed  of  an  outside  coating  of 
grey  matter  spread  in  a  continuous  and  uninterrupted  layer 
over  its  surface,  and  an  internal  core  of  white  matter.  The 
grey  coating  is  termed  the  cerebral  cortex,  whilst  the  white 
internal  part  is  called  the  medullary  centre.  Each  convolu- 
tion shows  a  corresponding  structure.  It  has  an  external 
covering  of  grey  matter  supported  upon  a  core  of  white 
medullary  matter.  But  in  addition  to  the  grey  matter  on  the 
outside,  there  are  certain  large  deposits  of  grey  matter  em- 
bedded in  the  substance  of  each  hemisphere  in  its  basal  part. 


464 


THE  BRAIN 


These  constitute  the  corpus  striatum,  and  although  to  a  certain 
extent  isolated  from  the  grey  matter  on  the  surface,  it  will  be 
observed  later  on  that  at  certain  points  they  are  directly 
continuous  with  it. 

By  means  of  the  convolutions  and  sulci  the  grey  matter 
on   the    surface   of  the   hemisphere   is  enormously  increased, 


Fig.   175. — Gyri  and  Sulci  on  the  Outer  Surface  of  the  Cerebral  Hemisphere. 


y.l   Sulcus  frontalis  superior. 

/I-  Sulcus  frontalis  inferior. 
/.in.  Sulcus  frontalis  medius. 
/.;;/.   Sulcus  paramedialis. 

A.  Pars  basilaris. 

B.  Pars  triangularis. 

C.  Pars  orbitalis. 
s.   Sylvian  fissure. 

s.1  Anterior    horizontal    limb   (Sylvian 

fissure). 
s.%  Ascending  limb  (Sylvian  fissure). 
s.Z  Posterior  horizontal    limb   (Sylvian 

fissure). 
p.C.i.    Inferior  praecentral  sulcus. 


/  c.s.  Superior  praecentral  sulcus. 
r.   Fissure  of  Rolando. 
g.s.    Superior  genu. 
g.i.   Inferior  genu. 
d.   Sulcus  diagonalis. 
/.I   Superior  temporal  sulcus  (parallel). 
t.'-  Inferior  temporal  sulcus. 
/.'   Inferior  post-central  sulcus. 
/.-  Superior  post-central  sulcus. 
/.:;  Ramus  horizontalis. 
/.4  Ramus  occipitalis. 
s.o.t.   Transverse  occipital  sulcus. 
cm.   Calloso-marginal  sulcus. 
c.t.r.   Inferior  transverse  furrow. 


without  unduly  adding  to  the  bulk  of  the  organ,  and  the 
vascular  pia  mater,  which  dips  into  every  fissure,  is  increased 
in  extent  to  a  like  degree.  Opportunity  is  therefore  afforded 
to  the  cortical  vessels  of  breaking  up  into  twigs  of  exceeding 
fineness  before  entering  the  substance  of  the  hemisphere. 
The  distribution  of  the  blood  to  the  grey  cortex  is  in  this  way 
equalised  and  rendered  uniform. 


THE  CEREBRUM  465 

Cerebral  Lobes  and  Interlobar  Fissures. — Certain  of  the 
fissures  which  traverse  the  surface  of  the  cerebrum  are 
arbitrarily  chosen  for  the  purpose  of  subdividing  the  surface 
into  districts,  termed  lobes.  These  fissures,  which  receive 
the  name  of  interlobar,  are  the  following — (1)  the  fissure  of 
Sylvius;  (2)  the  fissure  of  Rolando  ;  (3)  the  parieto-occipital ; 
(4)  the  calloso  -  marginal ;  (5)  the  collateral;  and  (6)  the 
limiting  sulcus  of  Reil. 

The  lobes  which  are  mapped  out  by  these  fissures  are — 
(1)  the  frontal;  (2)  the  parietal;  (3)  the  occipital;  (4)  the 
temporal ;  (5)  the  central,  or  island  of  Reil ;  (6)  the  falciform 
or  limbic.  To  these  may  be  added  a  seventh  lobe,  in  no  way 
related  to  the  interlobar  fissures,  viz.,  the  olfactory  lobe. 

Fissure  of  Sylvius. — This  is  the  most  conspicuous  fissure 
on  the  surface  of  the  cerebrum.  It  is  composed  of  a  short 
main  stem,  from  the  outer  extremity  of  which  three  branches 
radiate.  The  stem  of  the  Sylvian  fissure  is  placed  on  the 
inferior  surface  of  the  cerebrum  (Fig.  171).  It  begins  at 
the  locus  perforatus  anticus  in  a  deep  depression  called  the 
vallecula  Sylvii.  From  this  it  passes  horizontally  outwards, 
forming  a  deep  cleft  between  the  temporal  pole  and  the 
orbital  surface  of  the  frontal  lobe.  Appearing  on  the  outer 
surface  of  the  cerebrum,  the  Sylvian  fissure  immediately 
divides  into  three  radiating  branches.  These  are — (1)  the 
ramus  horizontalis  posterior ;  (2)  the  ramus  horizontalis 
anterior ;  and  (3)  the  ramus  ascendens  anterior. 

The  posterior  horizontal  limb  (Fig.  175)  is  the  longest  and 
the  most  conspicuous  of  the  three.  It  extends  backwards 
with  a  slight  inclination  upwards  for  a  distance  of  two  inches 
or  more  between  the  frontal  and  parietal  lobes  which  lie  above 
it,  and  the  temporal  lobe  which  is  placed  below  it.  Finally, 
it  comes  to  an  end  by  turning  upwards  into  the  parietal  lobe 
in  the  form  of  an  ascending  terminal  piece  (Fig.  175,  s.  asc). 

The  anterior  horizontal  limb  (Fig.  175)  extends  horizontally 
forwards  in  the  frontal  lobe  for  a  distance  of  about  three- 
quarters  of  an  inch  immediately  above  and  parallel  to  the 
posterior  part  of  the  superciliary  margin  of  the  hemisphere. 

The  ascending  limb  (Fig.  175)  proceeds  upwards  with  a 
slight  inclination  forwards  into  the  lower  part  of  the  outer 
surface  of  the  frontal  lobe  for  a  distance  of  about  an  inch. 
In  many  cases  the  two  anterior  limbs  spring  from  a  common 
stem  of  greater  or  less  length  (Fig.   175). 

VOL.   II — 30 


466  THE   BRAIN 

Limiting  Sulcus  of  Reil  (sulcus  circularis  Reilii). — If  the 
lips  of  the  posterior  horizontal  limb  of  the  Sylvian  fissure  be 
now  gently  but  widely  pulled  asunder,  the  island  of  Reil  or  the 
central  lobe  will  be  seen  at  the  bottom.  This  is  surrounded 
by  a  limiting  sulcus,  of  which  we  recognise  three  parts,  viz., 
an  upper  part  bounding  it  above,  a  lower  part  marking  it  off 
below,  and  an  anterior  part  limiting  it  in  front.  The  insula 
thus  mapped  out  is  somewhat  triangular  in  form. 

Opercula  Insulae. — The  present  is  a  good  time  to  study 
the  manner  in  which  the  insula  or  island  of  Reil  is  shut  off 
from  the  surface  of  the  hemisphere.  When  the  fissure  of 
Sylvius  is  held  widely  open,  it  will  be  observed  that  the  insula 
is  overlaid  by  portions  of  cerebral  cortex  which  appear  as  if 
they  were  undermined.  These  by  the  approximation  of  their 
margins  or  lips  form  the  three  limbs  of  the  fissure  of  Sylvius, 
and  are  termed  the  opercula  insula.  It  will  be  noticed  that 
the  limbs  of  the  Sylvian  fissure  cut  right  through  between 
the  different  opercula,  and  extend  from  the  surface  of  the 
hemisphere  to  the  surface  of  the  island  of  Reil.  The 
opercula  are  four  in  number,  and  are  named — (i)  temporal, 
(2)  fronto- parietal,  (3)  frontal,  and  (4)  orbital.  They  are 
easily  distinguished. 

The  temporal  operculum  extends  upwards  over  the  insula 
from  the  temporal  lobe  ;  it  forms  the  lower  lip  of  the  posterior 
horizontal  limb  of  the  Sylvian  fissure. 

The  fronto-parietal  operculum  is  carried  downwards  over 
the  insula  to  meet  the  temporal  operculum.  Its  margin 
forms  the  upper  lip  of  the  posterior  horizontal  limb  of  the 
fissure  of  Sylvius. 

The  frontal  operculum  (Fig.  175,  B)  is  the  small  triangular 
piece  of  cerebral  cortex  between  the  ascending  and  anterior 
horizontal  limbs  of  the  Sylvian  fissure.  It  is  sometimes 
termed  the  pars  triangularis. 

The  orbital  operculum  (Fig.  175,  C)  is  for  the  most  part  on 
the  under  surface  of  the  hemisphere.  It  lies  below  and  to 
the  inner  side  of  the  anterior  horizontal  limb  of  the  fissure  of 
Sylvius,  and  proceeds  backwards  from  the  orbital  aspect  of  the 
frontal  lobe  over  the  fore-part  of  the  insula. 

Fissure  of  Rolando  (sulcus  centralis).  —  The  fissure  of 
Rolando  takes  an  oblique  course  across  the  outer  convex 
surface  of  the  cerebral  hemisphere  (Fig.  175).  Its  upper 
end  cuts  the  supero-mesial  border  of  the  hemisphere  a  short 


THE  CEREBRUM  467 

distance  behind  the  mid-point  between  the  frontal  and  occipital 
poles,  whilst  its  lower  end  terminates  above  the  middle  of  the 
posterior  horizontal  limb  of  the  fissure  of  Sylvius.  Its  superior 
extremity,  as  a  rule,  turns  round  the  supero-mesial  border  of 
the  hemisphere,  and  is  then  continued  backwards  for  a  short 
distance  on  its  mesial  surface  (Fig.  176).  Although  in  its 
general  direction  the  fissure  of  Rolando  is  oblique,  it  is  far 
from  being  straight.  Nearer  to  its  upper  than  to  its  lower 
end  it  is  bent  backwards  so  as  to  form  a  bay,  within  which 
is  accommodated  a  portion  of  the  cerebral  cortex  which 
represents  the  motor  area  of  the  opposite  upper  limb.  The 
upper  and  lower  limits  of  this  bay  are  termed  the  upper  and 
lower  genua  of  the  fissure. 

Parieto  -  occipital  Fissure. —  A  very  small  part  of  this 
fissure  appears  on  the  outer  face  of  the  cerebral  hemisphere 
(Fig.  175).  For  the  most  part  it  is  situated  on  the  internal 
surface  (Fig.  176).  It  is  customary,  therefore,  to  describe 
an  external  parieto-occipital  and  an  internal  parieto-occipital 
fissure.  At  the  same  time,  it  must  be  clearly  understood 
that  they  are  directly  continuous  with  each  other  around  the 
supero-mesial  margin  of  the  hemisphere. 

The  external  parieto-occipital  fissure  cuts  the  supero-mesial 
border  of  the  hemisphere  in  a  transverse  direction  from  one 
and  a  half  to  two  inches  in  front  of  the  occipital  pole.  It  is 
usually  not  more  than  half  an  inch  in  length,  and  it  is  brought 
to  an  abrupt  termination  by  an  arching  convolution  which 
winds  round  its  extremity,  and  receives  the  convenient  name 
of  arcus  parieto-occipitalis  (Fig.  175). 

The  internal  parieto-occipital  fissure  (Fig.  176)  is  carried 
downwards  in  a  nearly  vertical  direction  as  a  conspicuous  and 
deep  cleft,  which,  by  its  lower  end,  runs  into  the  calcarine 
fissure. 

Collateral  Fissure  (Fig.  176). — The  sulcus  collateralis  is  a 
strongly  marked  fissure  on  the  tentorial  part  of  the  inferior 
surface  of  the  cerebral  hemisphere.  It  begins  near  the 
occipital  pole,  and  extends  forwards  towards  the  temporal 
pole  In  its  posterior  part  it  is  placed  below  and  parallel  to 
the  calcarine  fissure,  whilst  in  front  it  is  separated  from  the 
hippocampal  or  dentate  fissure  by  the  hippocampal  con- 
volution, i.e.,  the  innermost  convolution  on  the  tentorial 
surface  of  the  hemisphere  (Fig.  176). 

In  front  of  the  anterior  end  of  the  collateral  fissure  a  shallow 


468 


THE  BRAIN 


sulcus  will  be  seen  turning  round  the  anterior  end  of  the 
temporal  lobe  so  as  to  intervene  between  the  temporal  pole 
and  the  uncinate  or  hook-like  extremity  of  the  hippocampal 
gyrus.     This  is  the  incisura  tempo?-alis  or  ecto-rhinal  fissure. 

Calloso- marginal  Fissure  (Fig.  176). — This  is  a  strongly 
marked  sulcus  on  the  fore-part  of  the  mesial  surface  of  the 
hemisphere.  It  divides  the  front  portion  of  the  mesial  surface 
into  an  upper  marginal  and  a  lower  callosal  convolution,  and 
forms  on  this  aspect  the  lower  limit  of  the  frontal  lobe.  Be- 
ginning below  the  fore  end  of  the  corpus  callosum,  close  to  the 
locus  perforatus   anticus,   the   calloso-marginal  fissure   curves 


Fig.  176. — The  Gyri  and  Sulci  on  the  Mesial  Aspect  of  the 
Cerebral  Hemisphere. 

r.   Fissure  of  Rolando  ;  r.o.  Rostral  sulcus  ;  i.t.   Incisura  temporalis. 

round  the  genu  of  the  corpus  callosum,  and  then  extends 
backwards  to  a  point  a  short  distance  behind  the  middle  of 
the  supero-mesial  surface.  It  then  turns  upwards  and  cuts  the 
supero-mesial  margin  of  the  hemisphere  immediately  behind 
the  upper  end  of  the  fissure  of  Rolando  (Fig.  176).  The 
relation  presented  by  the  two  extremities  of  these  fissures  is 
such  that  they  can  both  be  readily  recognised,  either  when 
examined  on  the  outer  or  the  mesial  aspect  of  the  cerebrum. 
Boundaries  of  the  Frontal  Lobe. — The  frontal  is  the  largest 
of  the  cerebral  lobes.  On  the  outer  surface  of  the  hemisphere 
it  is  bounded  behind  by  the  fissure  of  Rolando,  and  below  by 
the  posterior  horizontal  limb  of  the  fissure  of  Sylvius.  On  the 
mesial  face  it  is  limited  by  the  calloso-marginal  fissure,  whilst 


THE  CEREBRUM 


469 


on   the   inferior   surface  of  the   hemisphere  the  stem  of  the 
fissure  of  Sylvius  forms  its  posterior  boundary. 

External   Surface   of  the   Frontal    Lobe. — On    the   outer 
surface  of  the  frontal  lobe  the  following  sulci  and  gyri  may  be 


recognised  : — 


Sulci 


Sulcus    prcecentralis    in- 
ferior. 

Sulcus    pnecentralis    su- 
perior. 

Sulcus  paramedialis. 

Sulcus  frontalis  superior. 

Sulcus  frontalis  medius. 

Sulcus  frontalis  inferior. 

Sulcus  diagonalis. 
c Sulcus  fronto-marginalis. 


Gyri 


Gyrus  frontalis  ascendens  (or 

gyrus  praecentralis). 
Gyrus  front-  f  Pars  superior, 
alis  superior\Pars  inferior. 
Gyrus  front-  f  Pars  superior, 
alis    medius  \Pars  inferior. 

f  Pars  basilaris. 
Gyrus  front-  '  Pars  triangu- 
alis  inferior."!      laris. 

^Pars  orbitalis. 


The  inferior  prtecefitral  furrow  (sulcus  praecentralis  inferior) 
(Fig.  175)  consists  of  a  vertical  and  a  horizontal  part,  and, 
when  present  in  a  well-marked  form,  it  presents  a  figure- 
like  the  letter  T  or  F.  The  vertical  portion  lies  in  front  of 
the  lower  part  of  the  fissure  of  Rolando,  whilst  the  horizontal 
portion  extends  obliquely  forwards  and  upwards  into  the  middle 
frontal  convolution. 

The  superior frcscentrai furrow  (sulcus  praecentralis  superior) 
(Fig.  175)  is  a  short  vertical  sulcus  which  lies  at  a  higher 
level  than  the  inferior  praecentral  furrow,  in  front  of  the  upper 
part  of  the  fissure  of  Rolando.  It  is  almost  invariably  con- 
nected with  the  hinder  end  of  the  superior  frontal  sulcus. 

The  ascending  frontal  convolution  (gyrus  centralis  anterior) 
is  a  long  continuous  gyrus  which  is  limited  in  front  by  the  two 
praecentral  furrows,  and  behind  by  the  fissure  of  Rolando.  It 
extends  obliquely  across  the  hemisphere,  from  the  supero- 
mesial  margin  above  to  the  posterior  horizontal  limb  of  the 
Sylvian  fissure  below  (Fig.  175). 

The  superior  frontal  sulcus  (sulcus  frontalis  superior)  (Fig. 
175)  extends  forwards  in  a  more  or  less  horizontal  direc- 
tion from  the  sulcus  praecentralis  superior. 

The  superior  frontal  gyrus  (gyrus  frontalis  superior)  (Fig. 
175)  is  the  narrow  convolution  between  the  supero-mesial 
border  of  the  hemisphere  and  the  superior  frontal  sulcus.  It 
takes  a  horizontal  course  forwards  to  the  frontal  pole. 

The  inferior  frontal  sulcus  (sulcus  frontalis  inferior)  (Fig. 
175)  occupies  a  lower  level  than  the  superior  furrow  of  the 
same  name.      Its  hinder  end  is  [dated   in    the   angle   between 


470  THE  BRAIN 

the  vertical  and  horizontal  parts  of  the  inferior  praecentral 
sulcus,  and  is  not  infrequently  confluent  with  one  or  other  of 
these.  It  proceeds  forwards  towards  the  superciliary  margin 
of  the  hemisphere,  and  ends  a  short  distance  from  this  in  a 
terminal  bifurcation. 

The  middle  fro?ital  gyrus  (gyrus  frontalis  medius)  (Fig. 
175)  is  the  broad  convolution  which  lies  between  the  superior 
and  inferior  frontal  furrows. 

The  inferior  frontal  gyrus  (gyrus  frontalis  inferior)  (Fig. 
175)  is  that  portion  of  the  outer  surface  of  the  frontal  lobe 
which  is  placed  in  front  of  the  inferior  praecentral  sulcus  and 
below  the  inferior  frontal  sulcus. 

The  sulcus  paramedians  (Fig.  175)  is  the  term  applied  to 
a  series  of  short  irregular  furrows  arranged  longitudinally, 
close  to  the  supero-mesial  border  of  the  hemisphere.  These 
rudimentary  sulci  partially  subdivide  the  superior  frontal  con- 
volution into  an  upper  and  lower  division,  and  are  of  interest 
in  so  far  that  they  are  best  marked  in  high  types  of  brain. 

The  middle  frontal  sulcus  (sulcus  frontalis  medius  ol 
Eberstaller)  (Fig.  175)  proceeds  horizontally  forwards  in  the 
fore-part  of  the  middle  frontal  convolution,  so  as  to  divide 
it  into  an  upper  and  a  lower  part  (Fig.  175).  When  it 
reaches  the  superciliary  margin  of  the  hemisphere  it  bifur- 
cates, and  its  terminal  branches  spread  out  widely  from  each 
other,  and  together  constitute  a  transverse  furrow  called  the 
sulcus  fronto-marginalis  (Wernicke). 

Owing  to  the  subdivision  of  the  superior  and  middle  frontal 
convolutions  in  the  manner  indicated,  the  convolutions  in  the 
anterior  part  of  the  outer  surface  of  the  frontal  lobe  are 
arranged  in  five  horizontal  tiers. 

The  ififerior  frontal  convolution  (gyrus  frontalis  inferior) 
possesses  a  special  interest  and  importance,  on  account 
of  the  localisation  within  it,  on  the  left  side,  of  the  speech- 
centre.  It  consists  of  an  upper  ?wn-opercular  and  a  lower 
opercular  portion.  The  latter  is  cut  up  into  three  parts  by 
the  two  anterior  limbs  of  the  fissure  of  Sylvius.  These  are 
termed  the  pars  basilaris,  the  pars  triangularis,  and  the  pars 
orbitalis. 

The  pars  basilaris  (Fig.  175)  is  that  part  which  lies  be- 
tween the  vertical  limb  of  the  inferior  prsecentral  sulcus  and 
the  ascending  limb  of  the  Sylvian  fissure.  It  forms  the 
anterior   portion  of  the  fronto-parietal   operculum,   and  it  is 


THE  CEREBRUM 


47i 


traversed  in  an  oblique  direction  by  a  shallow  but  constant 
furrow,  termed  the  sulcus  diagonalis  (Fig.   175). 

The  pars  triangularis  (Fig.    175)  is  simply  another  name 
for  the  frontal  operculum.      It  is  triangular  in  form,  and  lies 


I  [G.   177. — (jyri  and  Sulci  on  the  Tentorial  and  Orbital  Surfaces  of  the 
Cerebral  Hemispheres. 

between  the  ascending  and  anterior  horizontal  limbs  of  the 
Sylvian  fissure. 

The  pars  orbitalis  (Fig.  175)  is  placed  below  the  anterior 
horizontal  limb  of  the  fissure  of  Sylvius. 

Mesial  Surface  of  the  Frontal  Lobe. — On  this  aspect  of 
the  frontal  lobe  there  is  an  elongated,  more  or  less  continuous, 


472  THE  BRAIN 

convolution  called  the  gyrus  marginalis.  It  lies  between  the 
supero-mesial  border  of  the  hemisphere  and  the  calloso- 
marginal  fissure  (Fig.  176).  In  the  fore-part  of  this  gyrus  one 
or  two  curved  sulci  are  usually  present.  These  are  termed 
the  sulci  rostrales  (Fig.  176). 

Further,  the  posterior  part  of  the  marginal  convolution  is 
more  or  less  completely  cut  off  from  the  portion  which  lies 
in  front.  This  part  is  called  the  paracentral  lobule,  and  into 
it  the  upper  end  of  the  fissure  of  Rolando  is  prolonged,  as 
it  turns  over  the  supero-mesial  border  of  the  hemisphere 
(Fig.   176). 

Orbital  Surface  of  the  Frontal  Lobe. — On  this  aspect  of 
the  frontal  lobe  there  are  two  sulci — viz.,  the  olfactory  and 
the  orbital. 

The  olfactory  sulcus  (Fig.  177)  is  a  straight  furrow  which 
runs  parallel  to  the  mesial  border  of  the  hemisphere.  It  is 
occupied  by  the  olfactory  tract  and  bulb,  and  it  cuts  off  a 
narrow  strip  of  the  orbital  surface  close  to  the  mesial  border 
which  receives  the  name  of  gyrus  rectus  (Fig.  177). 

The  orbital  sulcus  (tri-radiate  sulcus  of  Turner)  is  a  com- 
pound furrow  which  assumes  many  different  forms.  Most 
frequently  it  takes  the  shape  of  the  letter  H,  and  we  then 
recognise  three  component  parts — viz.,  an  external  limb,  an 
internal  limb,  and  a  transverse  limb. 

The  external  limb  (sulcus  orbitalis  externus)  curves  round 
the  orbital  part  of  the  inferior  frontal  gyrus,  so  as  to  limit  it 
internally.  The  internal  limb  (sulcus  orbitalis  internus)  marks 
off  a  convolution  between  itself  and  the  olfactory  sulcus  which 
receives  the  name  of  gyrus  orbitalis  internus.  The  transverse 
limb  (sulcus  orbitalis  transversus)  takes  a  curved  course  with 
the  concavity  directed  backwards.  It  divides  the  district 
between  the  external  and  internal  limbs  into  an  anterior 
part,  or  gyrus  orbitalis  anterior,  and  a  posterior  part,  or  gyrus 
orbitalis  posterior.  The  latter  corresponds  with  the  greater 
part  of  the  orbital  operculum  (Fig.  177). 

Boundaries  of  the  Parietal  Lobe. — The  parietal  lobe  forms 
a  considerable  part  of  the  external  face  of  the  cerebral  hemi- 
sphere, and  it  also  appears  on  the  mesial  face  in  the  form  of 
the  precuneus  or  quadrate  lobule.  In  front,  it  is  bounded 
by  the  fissure  of  Rolando,  which  separates  it  from  the  frontal 
lobe.  Below,  it  is  bounded  in  its  fore-part  by  the  posterior 
horizontal  limb  of  the  Sylvian  fissure.      Behind  the  upturned 


THE  CEREBRUM 


473 


end  of  this  fissure,  it  is  quite  continuous  inferiorly  with  the 
temporal  lobe,  and  an  arbitrary  line  drawn  backwards  on  the 
surface  of  the  brain  in  continuation  of  the  horizontal  part  of 
the  posterior  limb  of  the  fissure  of  Sylvius  is  taken  as  its 
inferior  limit  (Fig.  175).  Posteriorly,  it  is  separated  from  the 
occipital  lobe  at  the  supero-mesial  border  of  the  hemisphere 
by  the  external  parieto-occipital  fissure.  Below  this  it  is  more 
or  less  directly  continuous  with  the  occipital  lobe,  and  an 
arbitrary  line  drawn  across  the  outer  surface  of  the  hemisphere 
from  the  extremity  of  the  external  parieto-occipital  fissure  to 
an  indentation  on  the  infero-lateral  border  of  the  hemisphere, 
termed  the  preoccipital  notch,  may  be  regarded  as  furnishing 
a  posterior  limitation.  The  preoccipital  notch  is,  as  a  rule, 
only  visible  in  brains  that  have  been  hardened  in  situ.  It  is 
produced  by  a  slight  wrinkle  or  fold  of  the  dura  mater  on  the 
deep  aspect  of  the  parieto-mastoid  suture,  and  in  relation  to 
the  portion  of  the  lateral  venous  sinus  which  lies  in  this 
locality.  The  notch  is  placed  on  the  infero-lateral  border  of 
the  hemisphere,  about  one  inch  and  a  half  in  front  of  the 
occipital  pole. 

Mesial  Surface  of  the  Parietal  Lobe — Precuneus. — On 
the  mesial  surface  of  the  hemisphere  the  parietal  lobe  is 
represented  by  the  precuneus  or  quadrate  lobule.  This  district, 
which  is  somewhat  quadrilateral  in  form,  lies  between  the 
upturned  hinder  end  of  the  calloso-marginal  fissure  and  the 
internal  parieto-occipital  fissure.  Below,  it  is  imperfectly 
separated  from  the  limbic  lobe  by  a  somewhat  variable  sulcus 
called  the. post-limbic sulcus  (Fig.  176). 

External  Surface  of  the  Parietal  Lobe. — The  gyri  and 
sulci  on  the  outer  surface  of  the  parietal  lobe  are  the 
following : — 


Gyri 


'Ascending  parietal  or 
postcentral. 

Superior  parietal  lobule. 
Inferior  (  Supra-marginal, 
parietal-  Angular. 
lobule.    I  I'ost parietal. 


Sulci 


Intra- 

parietal 

Sulcus    postcentrals 

inferior. 
Sulcus    postcentralis 

of 
Turner. 

superior. 
Ramus  horizonlalis. 

Jpturned 
(a.)S 
(d.)  P 
[c.)S 

^ Ramus  occipitalis. 

ends  of — 

ylvian. 

arallel. 

econd  temporal. 

Intraparietal  Sulcus  of  Turner. —  This  is  a  composite 
sulcus  built  up  out  of  four  originally  distinct  factors.  Two  of 
these,  termed  the   sulcus   postcentralis   inferior  and  the  sulcus 


474  THE  BRAIN 

postcentral  superior,  take  a  more  or  less  vertical  course 
across  the  hemisphere,  and  are  most  frequently  continuous 
with  each  other.  The  other  two  factors  are  placed  horizon- 
tally one  behind  the  other,  and  they  are  called  the  ramus 
horizontalis  and  the  ramus  occipitalis. 

The  sulcus  postcentralis  inferior  (Fig.  175)  lies  behind 
the  lower  part  of  the  fissure  of  Rolando,  whilst  the  sulcus 
postcentralis  superior  (Fig.  175)  occupies  a  similar  position 
in  relation  to  the  upper  part  of  that  fissure.  When  confluent 
with  each  other  they  form  a  long  continuous  furrow,  which 
stretches  across  the  hemisphere  behind  the  fissure  of  Rolando 
and  parallel  to  it  (Fig.  175). 

The  ramus  horizontalis  (Fig.  175)  is  continuous  with  the 
upper  end  of  the  sulcus  postcentralis  inferior,  and  extends 
backwards,  with  a  slight  inclination  upwards,  between  the 
superior  parietal  lobule,  which  lies  above  it,  and  the  inferior 
parietal  lobule,  which  lies  below  it.  With  the  two  confluent 
postcentral  sulci  it  presents  a  figure  like  the  letter  —\  placed 
on  its  side. 

The  ramus  occipitalis  (Fig.  175)  is  a  curved  sulcus 
which  bounds  externally  the  arcus  parieto-occipitalis,  or,  in 
other  words,  the  arching  convolution  which  surrounds  the 
external  parieto  -  occipital  fissure.  Sometimes  the  ramus 
occipitalis  is  linked  on  to  the  ramus  horizontalis — more  fre- 
quently it  is  separate.  Its  posterior  end  runs  into  the  occipital 
lobe,  and  behind  the  arcus  parieto-occipitalis  it  bifurcates  into 
two  widely-spread-out  branches.  These  form  a  short  trans- 
verse fissure  in  the  occipital  lobe,  termed  the  sulcus  occipitalis 
transversus  (Ecker)  (Fig.  175). 

The  upturned  ends  of  the  posterior  horizontal  limb  of  the 
fissure  of  Sylvius  (Fig.  175,  s.  asc),  of  the  parallel  or  first  tem- 
poral fissure  (Fig.  175,  t.1  asc),  and  of  the  second  temporal 
sulcus  (Fig.  175,  t.'2  asc.)  extend  for  a  short  distance,  one 
behind  the  other,  into  the  inferior  parietal  lobule. 

Gyri  on  the  External  Surface  of  the  Parietal  Lobe. — The 
intraparietal  sulcus  maps  out  three  districts  or  areas  on  the 
outer  surface  of  the  parietal  lobe.  These  are  the  ascending 
parietal  convolution  and  the  superior  and  inferior  parietal 
lobules. 

The  ascending  parietal  convolution  ox  gyrus  centralis  posterior 
(Fig.  175)  is  a  long  gyrus  which  extends  obliquely  across 
the  hemisphere  from  the  supero-mesial  border  above  to  the 


THE  CEREBRUM  475 

posterior  limb  of  the  Sylvian  fissure  below.  In  front,  it  is 
bounded  by  the  fissure  of  Rolando,  and  behind  by  the 
superior  and  inferior  postcentral  furrows. 

The  superior  parietal  lobule  is  the  area  of  cerebral  cortex 
which  lies  between  the  ramus  horizontalis  below  and  the 
supero-mesial  border  of  the  hemisphere  above.  In  front,  it 
is  bounded  by  the  superior  postcentral  sulcus ;  whilst  behind, 
it  is  connected  with  the  occipital  lobe  by  the  arcus  parieto- 
occipitalis.  It  is  continuous  around  the  supero-mesial  border 
of  the  hemisphere  with  the  precuneus. 

The  inferior  parietal  lobule  lies  below  the  ramus  horizon- 
talis and  the  ramus  occipitalis,  and  behind  the  inferior  post- 
central furrow.  It  is  more  or  less  directly  continuous  with 
the  occipital  lobe  behind  and  the  temporal  lobe  below. 
From  before  backwards  it  presents  three  arching  convolutions, 
viz.,  the  supra-marginal,  the  angular,  and  the  post-parietal. 

The  supra-marginal  convolution  (Fig.  175)  is  folded  round 
the  upturned  end  of  the  posterior  limb  of  the  fissure  of 
Sylvius,  and  stands  in  continuity  with  the  first  temporal  con- 
volution. The  angular  gyrus  (Fig.  175)  arches  over  the  up- 
turned end  of  the  parallel  or  first  temporal  sulcus,  and  is 
continuous  with  the  second  temporal  convolution.  The  post- 
parietal  convolution  (Fig.  175)  winds  round  the  upturned  end 
of  the  second  temporal  sulcus,  and  runs  into  the  third 
temporal  gyrus. 

Boundaries  of  the  Occipital  Lobe. — The  occipital  lobe 
forms  the  hinder  pyramidal  part  of  the  cerebral  hemisphere, 
and  it  may  be  defined  as  being  that  portion  of  the  hemi- 
sphere which  encloses  the  posterior  horn  of  the  lateral 
ventricle.  On  the  surface  it  is  very  imperfectly  mapped  off 
from  the  parietal  and  temporal  lobes  which  lie  in  front  of  it. 
Being  pyramidal  in  form,  it  presents  three  surfaces  and  an 
apex  or  occipital  pole.  On  the  mesial  aspect  of  the  hemi- 
sphere it  is  separated  from  the  parietal  lobe  {i.e.,  the 
precuneus)  by  the  internal  parieto-occipital  fissure.  On  the 
tentorial  or  inferior  surface  it  is  not  marked  off  in  any  way 
from  the  temporal  lobe  and  the  hippocampal  part  of  the 
limbic  lube  which  lie  in  front  of  it.  It  is  necessary,  therefore, 
on  this  aspect,  to  employ  an  arbitrary  line  of  demarcation  ; 
one  which  extends  from  the  preoccipital  notch  on  the  infero- 
latcral  border  of  the  hemisphere  to  the  isthmus  of  the  limbic 
lobe    (i.e.,    the   narrow   part   of    the   limbic    lobe    immediate])' 


476  THE  BRAIN 

below  the  hinder  end  of  the  corpus  callosum)  will  serve 
the  purpose.  On  the  external  surface  the  external  parieto- 
occipital fissure  and  an  arbitrary  line  from  this  to  the  pre- 
occipital notch  may  be  regarded  as  separating  the  occipital 
from  the  parietal  and  temporal  lobes. 

Mesial  Aspect  of  the  Occipital  Lobe. — On  this  surface  we 
find  (i)  the  calcarine  fissure:  (2)  the  cuneus;  and  (3)  the 
gyrus  lingualis. 

The  calcarine  fissure  begins  on  the  occipital  pole  by  a 
bifurcated  extremity  which  lies  in  the  groove  which  is  formed 
on  this  part  of  the  brain  by  the  lateral  sinus.  From  this 
it  pursues  a  slightly  arched  course  forwards,  and  ends  by 
cutting  into  the  limbic  lobe  immediately  below  the  thickened 
posterior  extremity  (splenium)  of  the  corpus  callosum.  The 
calcarine  fissure  is  joined  by  the  internal  parieto-occipital 
fissure  at  a  point  somewhat  nearer  its  anterior  than  its 
posterior  extremity.  Together  the  two  fissures  present  a 
>--shaped  figure. 

If  the  calcarine  and  internal  parieto-occipital  fissures  be  fully  opened 
up,  so  as  to  expose  the  bottom  in  each  case,  two  well-marked  deep  or 
submerged  gyri  will  be  displayed  (Fig.  178).  One  of  these,  the  gyrus 
cunei,  marks  off  the  parieto-occipital  fissure  from  the  calcarine  fissure  ;  the 
other  interrupts  the  calcarine  fissure  immediately  behind  its  junction  with 
the  parieto-occipital.  It  is  called  the  anterior  cuneo-lingual  deep  gyrus, 
and  it  divides  the  calcarine  fissure  into  an  anterior  and  a  posterior  part. 
The  anterior  calcarine  fissure  corresponds  very  nearly  to  the  stem  of  the 
>- -shaped  fissural  arrangement.  It  is  very  deep,  and  being  a  complete 
fissure,  it  gives  rise  to  an  elevation  on  the  inner  wall  of  the  posterior  horn 
of  the  lateral  ventricle,  called  the  calcar  avis  or  the  hippocampus  minor. 
The  posterior  calcarme  fissure  is  much  shallower. 

The  cuneus  (Fig.  176)  is  the  wedge-shaped  or  triangular 
district  on  the  mesial  aspect  of  the  occipital  lobe  which  lies 
between  the  internal  parieto-occipital  and  calcarine  fissures. 

The  gyrus  lingualis  (Fig.  176)  is  a  well-marked  convolution 
between  the  calcarine  fissure  above  and  the  posterior  part  of 
the  collateral  fissure  below,  which  stretches  forwards  from  the 
occipital  pole.  Anteriorly  it  becomes  very  narrow,  and  joins 
the  hippocampal  part  of  the  limbic  lobe.  It  lies  partly  on 
the  mesial  and  partly  on  the  tentorial  surface  of  the  occipital 
lobe. 

Tentorial  Surface  of  the  Occipital  Lobe. — On  this  aspect 
there  is  only  one  convolution,  viz.,  the  posterior  part  of  the 
occipitotemporal  gyrus  (Fig.  177).  It  proceeds  continuously 
forwards  into  the  temporal   lobe   on    the   outer   side   of  the 


THE  CEREBRUM 


477 


collateral  fissure,  and  it  is  bounded  externally  by  the  occipito- 
temporal sulcus — a  furrow  which  is  rarely  continuous,  but  is 
usually  represented  by  a  series  of  detached  pieces. 

External  Surface  of  the  Occipital  Lobe. — There  are  two 
well-marked  sulci  on  this  face  of  the  occipital  lobe — viz.,  the 
sulcus  occipitalis  transversus  and  the  sulcus  occipitalis  lateralis 
or  sulcus  lunatus  of  Elliot  Smith. 

The  sulcus  occipitalis  transversus  (Fig.  175)  extends  trans- 
versely across  the  upper  part  of  the  lobe  behind  the  arcus 
parieto-occipitalis.  It  has  already  been  described  as  the 
terminal  bifurcation  of  the  ramus  occipitalis  of  the  intra- 
parietal  sulcus. 


Precuneus 


Internal  parieto- 
occipital fissure 


Cuneus- 

Anterior  cuneo- 
lingual  deep  gyrus 

Posterior  cuneo- 
lingual  deep  gyrus 


Callosal  gyrus 
Corpus  callosum 

Optic  thalamus 
Gyrus  cunei 

-Gyrus  lingualis 

Anterior  part  of  the 
^calcarine  fissure 


Fig.  178. — Posterior  Part  of  Inner  Surface  of  the  Left  Hemi- 
sphere. The  calcarine  and  the  internal  parieto-occipital 
fissures  are  widely  opened  up  so  as  to  show  the  deep  gyri 
within  them. 


The  sulcus  occipitalis  lateralis  (Fig.  175)  is  a  short 
horizontal  furrow  which  divides  the  outer  surface  of  the  lobe 
into  an  upper  and  a  lower  area  of  very  nearly  equal  extent. 
These  areas  are  connected  by  means  of  superficial  annectant 
gyri  with  the  parietal  and  temporal  lobes. 

Boundaries  of  the  Temporal  Lobe. — The  temporal  lobe  lies 
behind  the  stem  and  below  the  posterior  horizontal  limb  of 
the  fissure  of  Sylvius.  It  is  somewhat  pyramidal  in  form,  and 
presents  an  upper,  an  outer,  and  a  tentorial  surface,  with  a 
free  projecting  apex  or  pole.  Above,  it  is  bounded  by  the 
posterior  horizontal  limb  of  the  fissure  of  Sylvius,  together 
with  the  artificial  line  which  is  drawn  backwards  from  this. 
On  the  tentorial  surface  it  is  separated  from  the  hippocampal 
part  of  the  limbic  lobe  by  the  collateral  fissure  ;   whilst  behind, 


478  THE  BRAIN 

it  is  marked  off  from  the  occipital  lobe  by  the  arbitrary  lines 
already  described  (p.  475).  The  apex  or  temporal  pole  pro- 
jects forwards  on  the  under  surface  of  the  brain  beyond  the 
stem  of  the  Sylvian  fissure.  It  should  be  noticed  that  the 
recurved  extremity  of  the  hippocampal  part  of  the  limbic 
lobe  (uncus)  which  lies  to  the  inner  side  of  the  temporal  pole 
does  not  project  so  far  forwards  as  the  latter,  and  is  separated 
from  the  pole  by  the  incisura  temporalis  or  ecto-rhinal fissure. 

Upper  or  Opercular  Surface  of  the  Temporal  Lobe. — This 
is  the  surface  of  the  temporal  operculum  which  is  opposed  to 
the  island  of  Reil  and  the  fronto-parietal  operculum.  The 
fissure  of  Sylvius  must  therefore  be  widely  opened  up  to 
expose  it.  For  the  most  part  the  surface  is  smooth,  but 
towards  its  back  part  there  are  a  few  shallow  transverse 
furrows,  called  the  sulci  of  Heschl,  whilst  in  front,  on  the  deep 
aspect  of  the  temporal  pole,  two  or  three  furrows  are  also 
evident. 

Outer  Surface  of  the  Temporal  Lobe. — On  this  aspect  of 
the  lobe  there  are  two  horizontal  sulci,  called  respectively 
the  first  temporal,  or  parallel,  and  the  second  temporal 
sulcus. 

The  parallel  sulcus  (Fig.  175)  is  a  long  continuous  and 
deep  fissure  which  begins  near  the  temporal  pole,  and 
proceeds  backwards  below  the  posterior  limb  of  the  Sylvian 
fissure.  Its  hinder  end  turns  upwards  into  the  parietal  lobe, 
and  is  surrounded  by  the  angular  gyrus. 

The  second  temporal  sulcus  is  placed  midway  between  the 
parallel  sulcus  and  the  infero-lateral  border  of  the  hemisphere. 
It  is  very  rare  to  find  it  in  the  form  of  a  continuous  cleft. 
Usually  it  is  broken  up  into  several  isolated  pieces,  placed 
one  behind  the  other.  Its  hinder  part,  which  turns  up- 
wards into  the  parietal  lobe  (Fig.  175),  and  is  surrounded  by 
the  post-parietal  gyrus,  lies  close  to  the  artificial  line  of 
demarcation  between  the  occipital  and  parietal  lobes. 

By  the  two  temporal  sulci  the  outer  surface  of  the  temporal 
lobe  is  mapped  out  into  three  tiers  of  horizontal  convolutions, 
which  are  termed  the  first,  second,   and  third  te?nporal  gyri 

(Fig-  i75> 

Tentorial  Surface  of  the  Temporal  Lobe. — On  this  surface 
there  is  one  fissure,  termed  the  occipito-temporal  sulcus. 

The  occipito-temporal  sulcus  (Fig.  177)  lies  to  the  outer 
side  of  the   collateral  fissure  and   close  to  the  infero-lateral 


THE  CEREBRUM 


479 


border  of  the  hemisphere.  It  runs  in  an  antero-posterior 
direction,  and  is  not  confined  to  the  temporal  lobe,  but 
extends  backwards  towards  the  occipital  pole.  It  is  usually 
broken  up  into  two  or  more  separate  pieces. 

The    occipitotemporal   convolution    (Fig.    177)    is    situated 
between  the  collateral  fissure  and  the  occipito-temporal  sulcus. 

S.R.-r. 


S.R./. 


Fig.  179. — Fissures  and  Gyri  on  the  Surface  of  the  Insula. 
( Eberstaller. ) 


t,  2,  and  3.  Three  short  gyri  on  the  frontal 

part  of  the  insula. 
4  and  5.  Two  long  gyri  on  parietal  part. 
S.R.#.  Anterior  limiting  sulcus. 
S.R.s.  Superior  limiting  sulcus. 
S.R./.    Inferior  limiting  sulcus. 
L.   Limen  insula:. 
P.    I'ole  of  the  insula. 


F.    Orbital  operculum  (for  the  most  part 

removed). 
T.  Temporal  pole. 
Ti.  First  temporal  gyrus. 
T2.  Second  temporal  gyrus. 
x.y.  Gyri  of  Heschl. 
s.i.   Sulcus  centralis  insula;. 
s.a.   Sulcus  praecentralis  insula,-. 
in.   ( lyri  on  deep  surface  of  temporal  pole. 


It  extends  from  the  occipital  pole  behind  to  the  temporal 
pole  in  front. 

The  narrow  strip  of  surface  on  the  outer  side  of  the 
occipito-temporal  sulcus  is  continuous  round  the  infero-lateral 
margin  of  the  hemisphere  with  the  third  temporal  convolution 
on  the  outer  surface  of  the  cerebrum,  and  may  be  reckoned 
as  a  part  of  it. 

The  three  temporal  convolutions  and  the  occipito-temporal 
convolution  run  into  each  other  at  the  temporal  pole. 


480  THE  BRAIN 

Island  of  Reil  or  Insula. — The  insula  is  a  triangular  field 
of  cerebral  cortex  which  lies  on  a  deeper  plane  than  the 
general  surface  of  the  hemisphere,  and  is  hidden  from  view 
by  the  four  opercula  which  overlap  it  (p.  466).  It  is  bounded 
by  a  distinct  limiting  sulcus  (sulcus  circularis  Reilii),  which 
has  already  been  described ;  and  its  dependent  apical  part 
or  pole  which  looks  downwards,  is  in  close  relation  to  the 
Sylvian  vallecula  and  the  anterior  perforated  spot  on  the  base 
of  the  brain. 

The  insula  is  divided  into  several  diverging  convolutions 
by  a  series  of  radiating  sulci.  Of  the  latter,  one,  which 
presents  the  same  direction  and  lies  in  the  same  plane  as  the 
fissure  of  Rolando,  receives  the  name  of  the  sulcus  centralis 
insulce.  It  divides  the  insula  into  an  anterior  frontal  part  and 
a  posterior  parietal  portion. 

Olfactory  Lobe.  —  The  olfactory  lobe  is  small  and  rudi- 
mentary in  the  human  brain.  It  comprises  (1)  the  olfactory 
bulb  and  tract  with  the  two  roots  of  the  latter,  and  (2)  the 
trigonum  olfactorium. 

The  olfactory  tract  is  a  narrow  white  prismatic  band,  which 
expands  anteriorly  into  a  swollen  bulbous  extremity  termed 
the  olfactory  bulb.  Both  the  tract  and  the  bulb  lie  upon  the 
olfactory  sulcus  on  the  orbital  surface  of  the  frontal  lobe, 
whilst  the  inferior  surface  of  the  bulb  rests  on  the  cribriform 
plate  of  the  ethmoid  bone,  and  receives  the  numerous  olfactory 
nerves  which  reach  it  through  the  foramina  in  that  part  of 
the  cranial  floor. 

Posteriorly,  the  olfactory  tract  will  be  seen  to  divide  into 
two  diverging  roots  of  attachment.  The  mesial  root  curves 
abruptly  inwards,  and  may  be  followed  into  the  extremity  of 
the  callosal  and  sub-callosal  gyri.  The  lateral  root  runs  back- 
wards and  outwards  over  the  outer  part  of  the  locus  perforatus 
anticus,  and  gradually  disappears  from  view.  In  animals,  in 
which  the  olfactory  apparatus  is  better  developed  than  in 
man,  it  may  be  traced  into  the  uncinate  extremity  of  the 
hippocampal  convolution. 

The  gyrus  sub-callosus  is  a  narrow  cortical  strip,  of  some  morphological 
importance,  which  lies  in  the  mesial  surface  of  the  hemisphere  immediately 
below  the  genu  of  the  corpus  callosum. 

The  trigonum  olfactorium  is  the  little  triangular  field  of 
grey  matter  which  occupies  the  interval  between  the  roots  of 
the  olfactory  tract  at  the  point  where  they  begin  to  diverge. 


THE  CEREBRUM  481 

Limbic  or  Falciform  Lobe. — This  lobe  is  seen  on  the 
mesial  surface  of  the  hemisphere,  in  the  form  of  an  elongated 
ring-like  convolution,  the  extremities  of  which  approach  closely 
to  each  other  at  the  locus  perforatus  anticus.  These  ex- 
tremities are  connected  by  the  roots  of  the  olfactory  tract, 
and  in  this  manner  the  limbic  ring  may  be  considered  to  be 
closed. 

The  upper  part  of  the  limbic  lobe  is  placed  in  intimate 
relation  to  the  extremities  and  upper  surface  of  the  corpus 
callosum,  and  receives  the  name  of  callosal  convolution  or  gyrus 
fornicatus.  The  lower  portion  of  the  lobe  is  termed  the 
hippocampal  convolution,  and  forms  the  inner  part  of  the 
tentorial  face  of  the  hemisphere.  The  continuity  between 
the  hippocampal  gyrus  and  the  callosal  convolution  is 
established  below  the  hinder  end  of  the  corpus  callosum 
posteriorly  by  a  narrow  portion  of  the  limbic  lobe  called  the 
isthmus.  From  this  point  the  hippocampal  gyrus  extends 
forwards  towards  the  temporal  pole.  Finally,  on  the  side  of 
the  crus  cerebri,  the  hippocampal  convolution  is  folded  back 
on  itself,  and  ends  in  a  recurved  hook-like  extremity,  termed 
the  uncus.  The  uncus  does  not  reach  so  far  forwards  as  the 
temporal  pole. 

The  callosal  convolution  begins  below  the  anterior  end  of 
the  corpus  callosum  at  the  locus  perforatus  anticus,  and,  wind- 
ing round  the  genu  of  the  callosum,  it  is  continued  backwards 
on  its  upper  surface  to  the  hinder  thickened  extremity  or 
splenium.  Finally,  curving  round  this,  it  becomes  greatly 
narrowed  through  the  calcarine  fissure  cutting  into  it.  This 
narrow  part  is  termed  the  isthmus,  and  constitutes  the  link  of 
connexion  between  the  callosal  gyrus  and  the  hippocampal 
gyrus. 

The  callosal  gyrus  is  separated  from  the  marginal  convolu- 
tion by  the  calloso-marginal  fissure.  Behind  this  it  is  im- 
perfectly marked  off  from  the  precuneus  by  the  post-limbic 
sulcus.  From  the  corpus  callosum  it  is  separated  by  the 
callosal  sulcus. 

The  hippocampal  convolution  is  bounded  on  the  outer  side 
by  the  anterior  part  of  the  collateral  sulcus,  and  in  front  of 
this  by  the  incisura  temporalis,  which  separates  its  hooked 
extremity,  or  uncus,  from  the  temporal  pole.  On  its  inner 
side  it  is  limited  by  the  hippocampal  or  dentate  fissure ; 
whilst  posteriorly  it  is  divided  into  two  parts  by  the  anterior 

vol.  11 — 31 


482  THE  BRAIN 

extremity  of  the  calcarine  fissure.  Of  these,  the  upper  is  the 
isthmus,  which  connects  it  with  the  callosal  gyrus,  whilst  the 
lower  portion  brings  it  into  direct  continuity  with  the  gyrus 
lingualis  or  infra-calcarine  convolution. 

If  the  dentate  fissure  which  lies  along  the  inner  side  of  the  hippocampal 
convolution  be  now  opened  up,  the  gyrus  dentatus  and  the  fimbria  lying 
side  by  side  will  be  brought  into  view. 

Fimbria  (Fig.  176). — This  is  simply  a  portion  of  the 
posterior  pillar  of  the  fornix  prolonged  into  this  region.  It  is 
a  conspicuous  band  of  white  matter,  which  presents  a  pro- 
minent free  border.  In  front,  it  runs  into  the  recurved  ex- 
tremity of  the  uncus,  whilst,  if  it  be  traced  backwards,  it  will 
be  seen  to  curve  upwards  behind  the  posterior  end  of  the 
optic  thalamus  and  become  continuous  with  the  posterior  pillar 
of  the  fornix  below  the  hinder  part  of  the  corpus  callosum. 

Gyrus  Dentatus  (dentate  fascia). — The  gyrus  dentatus  is 
the  free  edge  of  grey  matter  which  is  placed  between  the 
fimbria  and  the  deep  part  of  the  upper  surface  of  the  hippo- 
campal convolution.  The  groove  between  it  and  the  fimbria 
is  termed  the  fimbrio-dentate  sulcus.  It  is  slightly  notched 
along  the  margin,  whilst  its  surface  is  scored  by  numerous 
parallel  and  closely-placed  transverse  grooves.  It  begins 
behind  in  the  region  of  the  splenium  (the  thickened  posterior 
end  of  the  corpus  callosum),  and  it  is  carried  forwards  into 
the  cleft  of  the  uncus.  From  this  it  emerges  in  the  form  of 
a  delicate  band  which  crosses  the  surface  of  the  recurved 
part  of  the  uncus  in  a  transverse  direction,  thereby  consti- 
tuting the,  frenulum  Giacomini. 

Dentate  Fissure. — This  is  a  complete  fissure,  and  the 
elevation  on  the  ventricular  wall,  which  corresponds  to  it,  is 
called  the  hippocampus  major  (Fig.  176).  It  begins  behind 
the  splenium  of  the  corpus  callosum,  where  it  is  continuous 
with  a  shallow  part  of  the  callosal  fissure,  and  it  proceeds 
forwards  between  the  gyrus  dentatus  and  the  hippocampal 
convolution.      Its  anterior  end  is  enclosed  within  the  uncus. 

The  Corpus  Callosum. 

A  dissection  should  now  be  made  with  the  view  of  exposing 
the  upper  surface  of  the  corpus  callosum — the  commissural 
band  which  stretches  across  between  the  cerebral  hemispheres 
at  the  bottom  of  the  great  longitudinal  fissure. 


THE  CEREBRUM  483 

Dissection. — With  a  long  knife  slice  off  the  top  of  the  right  hemisphere 
at  the  level  of  the  calloso-marginal  fissure.  The  white  medullary  centre 
of  the  cerebral  hemisphere,  enclosed  on  all  hands  by  the  grey  cortex,  is 
brought  into  view,  and  the  appearance  receives  the  name  of  centrum  ovale 
minus.  From  the  central  white  mass  medullary  prolongations  proceed 
into  all  the  convolutions. 

A  transverse  incision  may  next  be  made  through  the  middle  of  the 
callosal  convolution,  and  insinuating  the  fingers  gently  under  it  the  dissector 
should  proceed  to  tear  it  away  from  the  hemisphere  in  an  outward 
direction.  If  this  be  carried  out  successfully,  the  manner  in  which  the 
fibres  of  the  corpus  callosum  enter  the  hemisphere  will  be  seen.  In  cases 
where  the  student  is  dissecting  the  brain  for  the  second  time,  the  knife 
should  not  be  used  at  all  in  carrying  out  this  dissection.  The  top  of  the 
hemisphere  down  to  the  level  of  the  calloso-marginal  fissure  should,  in  the 
first  instance,  be  torn  off,  and  then  the  callosal  convolutions  may  be  treated 
in  the  same  way.  By  this  expedient  the  fibres  of  the  callosum  may  be 
traced  into  the  convolutions. 

Cingulum. — If  the  deep  surface  of  the  callosal  convolution 
which  has  been  torn  away  be  examined,  a  large  bundle  of 
longitudinally  directed  fibres  will  be  noticed  embedded  in  its 
substance.  This  is  the  cingulum.  It  can  be  easily  dislodged  ; 
a  very  slight  degree  of  traction  is  all  that  is  required  to 
lift  it  out  of  its  bed.  In  front,  it  begins  at  the  locus  perforatus 
anticus,  whilst  behind,  it  turns  round  the  hinder  end  of  the 
callosum,  and  enters  the  hippocampal  convolution.  The 
cingulum  is  a  long  association  bundle  composed  of  several 
systems  of  fibres  which  only  run  for  short  distances  within  it. 
It  is  closely  associated  with  the  limbic  lobe. 

Dissection. — The  gyri  and  sulci  on  the  mesial  surface  of  the  left  hemi- 
sphere may  now  be  studied,  and  then  the  dissection,  which  has  been 
carried  out  with  the  view  of  exposing  the  corpus  callosum,  may  be  repeated 
on  the  left  side.  In  doing  this,  however,  take  care  not  to  injure  the  mesial 
surface  of  the  left  hemisphere  farther  back  than  the  parieto-occipital  fissure. 
Indeed,  an  effort  should  be  made  to  preserve  that  fissure  intact,  so  that  it 
and  the  cuneus  may  be  afterwards  studied  on  this  side  in  connexion  with 
the  gyri  and  sulci  on  the  under  surface  of  the  hemisphere. 

The  upper  surface  of  the  corpus  callosum  is  now  exposed,  and  it  will  be 
seen  that,  stretching  between  the  two  hemispheres,  it  unites  into  one  mass 
the  two  medullary  centres  of  the  two  hemispheres.  The  continuous  white 
field,  consisting  of  the  corpus  callosum  and  the  medullary  centre  of  each 
hemisphere,  receives  the  name  of  centrum  ovale  majus. 

Corpus  Callosum.  This  is  the  great  transverse  commissure 
of  the  cerebrum.  It  is  placed  nearer  the  anterior  than  the 
posterior  end  of  the  brain,  and  it  unites  the  inner  surfaces  of 
the  two  cerebral  hemispheres  throughout  very  nearly  a  half  of 
their  antero-posterior  length.  Looked  at  as  a  whole,  it  is 
arched  from  before  backwards,  and  presents  a  convex  upper 
surface  and  a  concave  lower  surface. 
11— .".1  a 


4§4 


THE  BRAIN 


The  upper  surface  of  the  corpus  callosum  forms  the  bottom 
of  the  great  longitudinal  fissure,  and  on  each  side  of  this  it 
is  covered  by  the  callosal  convolution.  Only  in  its  posterior 
part  is  it  touched  by  the  falx  cerebri ;  in  front,  this  process 
of  dura  mater  falls  considerably  short  of  it.  The  upper 
surface  of  the  callosum  is  coated  by  an  exceedingly  thin  layer 


Cingulum 
Fibres  of  corona  radiata  w  ^_ 


Intersection  of  (    " 
callosal  and  corona  | 


Frontal  fibres 
Genu 

-  Cut  surface 


radiata  systems  of  I        /&* 
fibres  [      K 


Corpus  callosum 


Transverse  fibres 
of  corpus 
callosum 


Cingulum ' 

Splenium 


Inferior  longitu- 
dinal fasciculus 


Tapetum 


Stria  longitudinalis  mesialis 


Fig.  180. — The  Corpus  Callosum  exposed  from  above  and  die  Right  Half 
dissected  to  show  the  course  taken  by  the  Fibres. 

of  grey  matter  continuous  at  the  bottom  of  the  callosal  sulcus 
with  the  grey  cortex  on  the  surface  of  the  hemisphere.  In 
this  are  embedded  on  either  side  of  the  mesial  plane  two 
delicate  longitudinal  bands  of  fibres  called  respectively  the 
stria  longitudinalis  mesialis  and  lateralis.  The  stria  lo?tgitu- 
dinalis  mesialis  is  the  more  strongly  marked  of  the  two,  and  it 
is  separated  from  its  fellow  of  the  opposite  side  by  a  faint 
mesial  furrow.  The  stria  longitudinalis  lateralis  is  placed 
farther  out.      So  thin  is  the  grey  coating  of  the  corpus  callosum 


THE  CEREBRUM 


485 


that  the  transverse  direction  of  the  bundles  of  callosal  fibres 
can  be  easily  seen  through  it. 

The  stride    with  the    thin  layer  of  grey  matter  associated  with   them 
represent  an  aborted  convolution  called  the  gyrus  supracallostis. 

The  two  extremities  of  the  corpus  callosum  (Fig.  181)  are 
greatly  thickened,  whilst  the  intermediate  part,  often  called 
the  body,  is  considerably  thinner.  The  massive  posterior  end, 
which  is  full  and  rounded,   lies  over  the  mesencephalon,  and 


Fig.  181. 

1.  Fornix. 

2.  Velum  interpositum. 

3.  Pineal  body. 

4.  Vena  magna  Galeni. 

5.  Splenium  of  corpus  cal- 

losum. 


9  s  7 

-Mesial  section  through  the  Brain. 


6.  Corpora  quadrigemina. 

7.  Valve  of  Vieussens. 

8.  Aqueduct  of  Sylvius. 

9.  Oculo-motor  nerve. 
10.  Corpus  mammillare. 
n.   Infundibulum. 


12.   Optic  commissure. 
1  ;.   Lamina  cinerea. 

14.  Anterior  commissure. 

15.  Foramen  of  Monro. 

16.  Genuofcorpuscallosuni. 

17.  Septum  Lucidum. 


extends  backwards  as  far  as  the  highest  point  of  the  cerebdlum. 
It  is  called  the  splenium.  The  anterior  end,  which  is  not 
quite  so  massive,  is  folded  downwards  and  backwards  upon 
itself,  and  is  called  the  genu.  The  recurved  lower  portion  of 
the  genu  is  separated  from  the  part  of  the  corpus  callosum 
which  lies  above  by  an  interval;  it  rapidly  thins  as  it  passes 
backwards,  and  is  termed  the  rostrum.  The  fine  terminal 
edge  of  the  rostrum  has  already  been  seen  to  be  connected 
with  the  lamina  einerea. 


486 


THE  BRAIN 


Both  the  lateral  and  the  mesial  longitudinal  striae,  when 
traced  backwards,  are  seen  to  turn  round  the  splenium,  and 
run  into  the  corresponding  gyrus  dentatus.  In  front,  the 
mesial  striae  are  carried  round  the  genu,  and  then  backwards 
on  the  under  surface  of  the  rostrum.  Finally,  each  stria 
runs  into  the  corresponding  gyrus  subcallosus.  Sometimes 
this  gyrus  is  termed  the  peduncle  of  the  corpus  callosum,  and 
the  fibres  of  the  stria  which  it  contains,  emerging  from  its 
substance,    proceed     backwards     and    outwards    along    the 

Genu  01 


Olfactory  tract -^ 


Optic  chiasma 
thrown  back 


Lamina  cinerea 
Peduncle  of  corpus 
;allosum 


Fig.  182. — Anterior  end  of  the  Corpus  Callosum  and  its 
Peduncles,  as  seen  from  below  when  the  frontal  lobes  of  the 
hemispheres  are  slightly  separated  from  each  other.  (From 
Cruveilhier. ) 

posterior   limit   of  the  anterior   perforated  spot   towards  the 
anterior  extremity  of  the  temporal  lobe. 

Fibres  of  the  Corpus  Callosum. —The  transverse  fibres  of  the  corpus 
callosum,  as  they  enter  the  white  medullary  centre  of  the  cerebral  hemisphere, 
radiate  from  each  other  so  as  to  reach  every  part  of  the  cerebral  cortex. 
This  radiation  is  called  the  radiatio  corporis  callosi.  The  more  anterior  of 
the  fibres  which  compose  the  genu  of  the  corpus  callosum  sweep  forwards 
in  a  series  of  curves  into  the  prefrontal  region  of  the  hemisphere.  A  large 
part  of  the  splenium,  forming  a  solid  bundle  termed  the  forceps  major,  bends 
suddenly  and  abruptly  backwards  into  the  occipital  lobe.  Fibres  from  the 
body  of  the  corpus  callosum  and  also  from  the  upper  part  of  the  splenium 
curving  round  the  lateral  ventricle  form  a  very  definite  stratum  called  the 
tapetum.  This  is  a  thin  layer  in  the  medullary  centre  of  the  hemisphere 
which  forms  the  roof  and  outer  wall  of  the  posterior  horn  and  the  outer 
wall  of  the  hinder  part  of  the  descending  horn  of  the  lateral  ventricle. 


THE  CEREBRUM 


487 


Lateral  Ventricle. 

The  lateral  ventricle  in  the  interior  of  the  cerebral  hemi- 
sphere should  now  be  opened  up  on  each  side.     The  corpus 

Genu  of  corpus  callosum 

■  r  oramen  of  Monro 


Ventricle  v. 
Septum  lucidum  j 


Corpus  callosum 
turned  to  left  side 


Caudate  nucleus 

Optic  thalamus 

Choroid  plexus 

■  /  Taenia  semicircularis 


Trigonum  ventriculi 
Hippocampus  major 
Posterior  pillar  of  fornix 


Calcar  avis 


liulb  of  comu 
Hippocampus  major 


I  'orceps  major 

Pody  of  fornix         Posterior  pillar  of  fornix 

Fig.  183.  -Dissection  to  show  the  Lateral  Ventricles.  The  body  of  the 
corpus  callosum  has  been  deta<  bed  from  the  genu  and  the  splenium  and 
turned  over  to  the  left. 

callosum,  which  forms  the  roof  of  the  body  and  anterior  horn 
of  this  cavity,  must  therefore  be  partially  removed, 
j  1 — :J1  l> 


488 


THE  BRAIN 


Dissection. — Make  a  longitudinal  incision  through  the  corpus  callosum 
about  half  an  inch  or  less  from  the  mesial  plane  on  each  side.  The  central 
portion  of  the  corpus  callosum  which  lies  between  these  incisions  is  to  be 
kept  in  position.  The  lateral  portions  must  be  turned  outwards  and 
detached  completely.  As  this  is  being  done,  it  will  become  evident  that  the 
lower  part  of  the  splenium  which  is  prolonged  into  the  forceps  major  is  in 
reality  a  portion  folded  forwards  in  close  apposition  with  the  under  surface 
of  the  hinder  end  of  the  corpus  callosum.  Be  careful  to  leave  the  forceps 
major  in  its  place. 

The  body  and  the  anterior  horn  of  the  ventricle  are  now  exposed  ;  but 
the  cavity  of  the  ventricle  is  carried  backwards  into  the  occipital  lobe  in 
the  form  of  a  posterior  horn,  and  downwards  and  forwards  into  the  temporal 


rRAL 


^ 


ANT?   COMMISSURE 


OPTIC  RECESS 


NFUNDiBULAR 
RECESS 


VENT.  J  V 


**&S*. 


Fig.  184. — Cast  of  the  Ventricles  of  the  Brain  (from  Retzius). 


R.SP.   Recessus  suprapinealis. 
R.P.     Recessus  pinealis  inferior. 


A.S.  Aqueduct  of  Sylvius. 
F.M.  Foramen  of  .Monro. 


lobe  in  the  form  of  the  descending  horn.  The  posterior  horn  can  only  at 
present  be  opened  on  the  right  side.  Carry  the  knife  backwards  through  the 
medullary  substance  which  forms  its  roof,  and  remove  a  sufficient  amount 
of  this  to  give  a  complete  view  of  the  interior  of  this  part  of  the  cavity. 
Greater  difficulty  will  be  experienced  in  opening  up  the  descending  horn. 
Place  the  point  of  the  knife  in  the  upper  part  of  the  horn  where  it  joins  the 
body  of  the  ventricle,  and  carry  the  blade  in  a  downward  and  forward 
direction  through  the  outer  part  of  the  temporal  lobe  towards  the  temporal 
pole,  following  the  course  of  the  cavity.  This  corresponds  very  nearly  with 
the  course  of  the  parallel  fissure.  The  outer  wall  of  the  descending  horn 
is  thus  incised,  and  a  sufficient  amount  of  the  outer  part  of  the  temporal 
lobe  must  be  removed  to  give  a  view  of  the  cavity.  In  doing  this,  the 
temporal  operculum  will  be  taken  away,  but  the  surface  of  the  insula  should 
be  preserved  from  injury. 


THE  CEREBRUM 


489 


Lateral  Ventricle. — The  dissector  will  now  perceive  that 
each  cerebral  hemisphere  is  hollow.      The  cavity  in  the  interior 

Caudate  nucleus 


Putamen 


Anterior  commissure   1 


Pes  hippocampi 

Hippocampus  major         ,' 
Descending  cornu  of 
lateral  ventricle 


_Genu  of  corpus 
callosum 


-y-'i'n  --Septum  lucidum 
Ventricle  v. 
■  — Caudate  nucleus 

foramen  of 
Monro 


1  aenia  semi- 
;ircularis 


Thalamus 
Fornix 


Medial  longi- 
"  tudinal  striae 


Choroid  ; 
plexus' 
Fimbria 
Posterior  collateral 
eminence 
Posterior  cornu 


~x^U 


Calcar  avis 


Forceps  major 

FlG.  JCJ5. — Dissection  to  show  the  Posterior  and  Descending  Cornua  of  the 
Lateral  Ventricle  on  the  left  side, 

is  called  the  lateral  ventricle,  and  is  lined  by  a  thin  dark- 
coloured  layer  of  epithelium,  which  is  termed  the  ependyma.  In 
certain  places  the  walls  are  in  apposition  with  each  other,  but  in 


490 


THE   BRAIN 


other  localities  spaces  of  varying  capacity,  and  containing 
cerebro-spinal  fluid,  are  left  between  the  bounding  walls.  The 
lateral  ventricle  communicates  with  the  third  ventricle  of  the 
brain  by  means  of  a  small  foramen,  just  large  enough  to  admit 
a  crow-quill,  which  is  termed  the  foramen  of  Monro.  This 
aperture  is  placed  in  front  of  the  fore  end  of  the  optic 
thalamus,  and  behind  the  anterior  pillar  of  the  fornix. 


Corpus  callosum 


Great  longitudinal  fissure 


Lateral  ventricle 

Choroid  plexus     ! 
Foramen  of  Monro       I 
Anterior  pillar  of  fornix 


Claustrum 

Internal  capsule 

Lenticular  nucleus 
I  Caudate  nucleus 

Septum  lucidum 


Fig.  186. — Coronal  section  through  the  Cerebrum  so  as  to  cut  through  the 
anterior  part  (putamen)  of  the  lenticular  nucleus.  The  anterior  cut 
surface  of  the  posterior  part  of  the  cerebrum  is  depicted. 

The  shape  of  the  lateral  ventricle  is  very  irregular,  and 
can  be  best  understood  by  the  study  of  a  plaster  cast  of 
its  interior  (Fig.  184).  It  is  usual  to  describe  it  as  being 
composed  of  a  body  and  three  horns,  viz.,  an  anterior,  a 
posterior,  and  a  descending  horn.  The  anterior  horn  is  that 
part  of  the  cavity  which  lies  in  front  of  the  foramen  of  Monro. 
The  body  is  the  portion  of  the  ventricle  which  extends  from 
the  foramen  of  Monro  to  the  splenium  of  the  corpus  callosum. 


THE  CEREBRUM  491 

At  this  point  the  posterior  and  descending  horns  diverge  from 
the  hinder  end  of  the  body.  The  posterior  horn  curves  back- 
wards and  inwards  into  the  occipital  lobe.  It  is  very  variable 
in  its  length  and  capacity.  The  descending  horn  proceeds  with 
a  bold  sweep  round  the  hinder  end  of  the  optic  thalamus, 
and  then  tunnels  in  a  forward  and  inward  direction  through 
the  temporal  lobe  towards  the  temporal  pole. 

Anterior  Horn  of  the  Lateral  Ventricle. — The  anterior 
horn  forms  the  foremost  part  of  the  cavity,  and  extends  in 
a  forward  and  outward  direction  in  the  frontal  lobe.  When 
seen  in  coronal  section  it  presents  a  triangular  outline — the 
floor  sloping  upwards  and  outwards  to  meet  the  roof  at  an 
acute  angle  (Fig.  186).  It  is  bounded  in  front  by  the 
posterior  surface  of  the  genu  of  the  corpus  callosum,  whilst 
the  roof  is  formed  by  the  fore-part  of  the  same  structure. 
The  inner  wall,  which  is  vertical,  is  formed  by  the  septum 
lucidum — a  thin  mesial  partition  between  the  lateral  ventricles 
of  opposite  sides.  The  sloping  floor  presents  a  marked  eleva- 
tion or  bulging,  viz.,  the  smooth  rounded  and  enlarged  anterior 
extremity  of  the  pear-shaped  caudate  nucleus. 

Body  of  the  Lateral  Ventricle. — The  body  of  the  ventricle 
is  likewise  roofed  by  the  corpus  callosum.  On  the  inner  or 
mesial  side  it  is  bounded  by  the  hinder  part  of  the  septum 
lucidum,  and  behind  this  by  the  attachment  of  the  fornix  to 
the  under  surface  of  the  corpus  callosum.  On  the  outer  side 
it  is  closed,  as  in  the  case  of  the  anterior  horn,  by  the  meeting 
of  the  roof  and  the  floor  of  the  cavity. 

On  the  floor  a  number  of  important  objects  may  be 
recognised.  From  without  inwards,  and,  at  the  same  time, 
to  some  extent  from  before  backwards,  these  are — (1)  the 
caudate  nucleus;  (2)  a  groove  which  extends  obliquely  from 
before  backwards  and  outwards  between  the  caudate  nucleus 
and  the  optic  thalamus,  and  in  which  are  placed  the  vein 
of  the  corpus  striatum  and  a  white  band  called  the  taenia 
semicircularis ;  (3)  a  portion  of  the  upper  surface  of  the 
optic  thalamus;  (4)  the  choroid  plexus;  (5)  the  thin  sharp 
lateral  edge  of  the  fornix. 

The  caudate  nucleus  as  it  proceeds  backwards  on  the  outer 
pail  of  the  floor  of  the  body  of  the  lateral  ventricle  narrows 
very  rapidly. 

The  vein  of  the  corpus  striatum  is  exposed  in  the  groove 
between  the  caudate  nucleus  and  the  optic  thalamus,  if  the 


492 


THE   BRAIN 


ependyma  which  covers  it  be  scraped  away.  It  joins  the 
vein  of  Galen  at  the  foramen  of  Monro.  In  the  same  groove 
is  placed  the  tarda  semicircularis — a  narrow  band  of  white 
matter,  which  in  the  region  of  the  foramen  of  Monro  bends 
downwards  and  disappears  from  view.  Its  fibres  ultimately 
reach  the  locus  perforatus  anticus,  in  which  they  end. 

The  portion  of  the  upper  surface  of  the  optic  thalamus, 
which  appears  in  the  floor  of  the  lateral  ventricle,  is  in 
great  part  covered  by  the  choroid  plexus  (plexus  choroideus 


Bulb  of  cornu 


Splenium 


Bulb  of  cornu 


v    Calcar  avis       Calcar  avis 
\  Tapetum 

\  Optic  radiation 
Inferior  longitudinal  bundle 

Fig.  187. — Coronal  section  through  the  Posterior  Horns  of  the 
Lateral  Ventricles. 


lateralis).  The  latter  is  a  rich  vascular  fringe  which  appears 
from  under  cover  of  the  sharp  lateral  edge  of  the  fornix. 
In  front,  it  is  continuous,  behind  the  foramina  of  Monro, 
with  the  corresponding  choroid  plexus  of  the  opposite  side ; 
whilst  behind,  it  is  carried  into  the  descending  horn  of  the 
ventricle.  Although  the  choroid  plexus  has  all  the  appear- 
ance of  lying  free  within  the  ventricle,  it  must  be  borne  in 
mind  that  it  is  invested  by  an  epithelial  layer  which  excludes 
it  from  the  cavity,  and  which  is  connected  on  the  one  hand 
to  the  sharp  margin  of  the  fornix,  and  on  the  other  to  the 
upper  surface  of  the  optic  thalamus. 

Posterior  Horn  of  the  Lateral  Ventricle. — The  posterior 


THE  CEREBRUM  493 

horn  is  a  diverticulum  carried  backwards  into  the  occipital 
lobe  from  the  hinder  end  of  the  body  of  the  ventricle.  It 
tapers  to  a  point  and  describes  a  gentle  curve,  the  convexity 
of  which  is  directed  outwards.  The  roof  and  outer  wall  of 
this  portion  of  the  ventricular  cavity  is  formed  by  the  tapetum 
of  the  corpus  callosum. 

Upon  the  inner  wall  two  elongated  curved  elevations  may 
be  observed.  The  uppermost  of  these  is  termed  the  bulb  of 
the  cornu  (bulbus  cornu  posterioris),  and  is  produced  by  the 
fibres  of  the  forceps  major  as  they  curve  abruptly  backwards 
from  the  lower  part  of  the  splenium  of  the  corpus  callosum 
into  the  occipital  lobe.  Below  this  is  the  elevation  known  as 
the  hippocampus  minor  or  the  calcar  avis.  It  varies  greatly  in 
size  in  different  brains,  and  is  caused  by  an  infolding  of  the 
ventricular  wall  in  correspondence  with  the  anterior  calcarine 
fissure  on  the  exterior  of  the  hemisphere. 

Dissection.  —  The  dissector  should  now  gently  insinuate  his  ringers 
underneath  the  fronto-parietal  operculum  of  the  insula  and  tear  this  portion 
of  the  cortex  away  in  an  upward  direction.  The  frontal  operculum  (pars 
triangularis)  and  the  orbital  operculum  should  be  dealt  with  in  the  same 
manner.  The  greater  part  of  the  temporal  operculum  has  already  been 
removed  in  opening  up  the  descending  horn  of  the  ventricle.  The  insula 
or  island  of  Reil  is  therefore  fully  exposed  to  view,  and  its  relation  to  the 
parts  in  the  interior  of  the  ventricle  can  be  seen. 

Descending  Horn  of  the  Lateral  Ventricle. — The  descending 
horn  must  be  regarded  as  the  direct  continuation  of  the  main 
ventricular  cavity  into  the  temporal  lobe.  The  posterior 
horn  is  merely  a  diverticulum  carried  backwards  from  the 
main  cavity.  At  first  directed  backwards  and  outwards,  the 
descending  horn  suddenly  sinks  downwards  behind  the  optic 
thalamus  into  the  temporal  lobe,"  in  which  it  takes  a  curved 
course  forwards  and  inwards  to  a  point  about  an  inch  behind 
the  extremity  of  the  temporal  pole.  In  the  angle  between  the 
diverging  descending  and  posterior  horns  the  cavity  of  the 
ventricle  exhibits  a  triangular  expansion  of  varying  capacitv. 
This  is  called  the  trigonum  ventriculi. 

The  roof  of  the  descending  horn  is  formed  for  the  most 
part  by  the  tapetum  of  the  corpus  callosum.  At  the  extremity 
of  the  horn  (he  roof  presents  a  slight  bulging  into  the 
ventricular  cavity.  This  is  the  amygdaloid  tubercle,  and  it  is 
produced  by  a  superjacent  collection  of  grey  matter,  termed 
the  amygdaloid  nucleus.  The  tcenia  semicircularis  and  the 
greatly  attenuated  tail  of  the  caudate  nucleus  are  both  prolonged 


494 


THE  BRAIN 


into  the  descending  horn,  and  are  carried  forwards  in  its  roof 
to  the  amygdaloid  nucleus. 

On  the  floor  of  the  descending  horn  the  dissector  will 
observe  the  following  parts  :  (i)  the  hippocampus  major;  (2) 
the  choroid  plexus;  (3)  the  fimbria;  and  (4)  the  eminentia 
collateralis. 

Hippocampus  Major  (cornu  ammonis). — This  is  for  the 
most  part  covered  by  the  choroid  plexus.  It  is  a  prominent 
elevation  on  the  floor  of  the  descending  horn  of  the  lateral 

Pes  hippocampi 
Hippocampus  major 

Anterior  collateral  eminence 


Uncus 

Frenulum  Giacomini 

Fimbria 

Gyrus  dentatus 

Fornix 

Hippocampal 
convolution 


Splenium   ■£ 


Trigonum  ventriculi       y 
Calcar  avis 


Posterior  horn 
P.ulb  of  cornu 


Fig.   188. — Dissection  to  show  the  Posterior  and  Descending  Cornua  of  the 

Lateral  Ventricle. 

ventricle,  and  is  strongly  curved  in  conformity  with  the  course 
taken  by  the  horn  in  which  it  lies.  It  therefore  presents  an 
internal  concave  border  and  an  external  convex  margin. 
Narrow  behind,  it  enlarges  as  it  is  traced  forwards,  and  it 
ends  below  the  amygdaloid  tubercle  in  a  thickened  extremity 
which  presents  some  faint  grooves  or  notches  on  its  surface. 
In  consequence  of  this,  the  anterior  end  of  the  hippocampus 
major  receives  the  name  of  the  pes  hippocampi.  The  hippo- 
campus major  is  the  internal  elevation  which  corresponds  to 
the  dentate  or  hippocampal  fissure  on  the  exterior  of  the 
cerebrum. 


THE  CEREBRUM 


495 


Fimbria  (taenia  hippocampi). — The  fimbria  is  a  narrow  but 
very  distinct  band  of  white  matter  which  is  attached  by  its 
outer  margin  along  the  concave  inner  border  of  the  hippocampus 


Body  of  lateral  ventricle 
Sylvian  grey  matter 
Aqueduct 
of  Sylvius 


Choroid  plexus 

Caudate  nucleus 

Optic  radiation 

Caudate  nucleus  (tail) 


Optic  radiation 
Inferior  longitudinal  bundle 
Tapetum 
\     ^Choroid  plexus 
Descending  horn  of  lateral  ventricle 
Alveus 


Lateral  fillet 


Internal  geniculate  body 
Hippocampal  convolution 


Hippocampus  major 
Fimbria 

Gyrus  dentatus 

External  geniculate  body 
Choroid  fissure 


Fig.  189. — Coronal  section  through  the  Cerebrum,  Mid-brain,  and  Pons  Varolii 
in  the  plane  of  the  geniculate  bodies.  It  shows  the  relation  of  the  dentate 
and  choroid  fissures  to  the  descending  horn  of  the  lateral  ventricle. 

major.  The  white  matter  composing  it  is  continuous  with 
the  thin  white  layer  (alveus)  which  is  spread  over  the  surface 
of  the  hippocampus  major,  and  it  presents  two  free  surfaces 
and  a  sharp  free  inner  border.     The  fimbria  has  already  been 


496  THE  BRAIN 

examined  in  connexion  with  the  hippocampal  fissure  and  the 
gyrus  dentatus,  and  the  relations  which  it  presents  to  the 
posterior  pillar  of  the  fornix  and  the  uncus  have  been  pointed 
out  (p.  482). 

Choroid  Fissure  of  the  Cerebrum. — When  the  pia  mater 
in  the  region  of  the  hippocampal  fissure  is  removed  from  the 
surface  of  the  brain,  the  choroid  plexus  in  the  interior  of  the 
descending  horn  of  the  lateral  ventricle  is  usually  withdrawn 
with  it,  and  a  fissure  appears  between  the  fimbria  and  the  roof 
of  the  ventricular  horn.  This  is  termed  the  choroid  fissure  of 
the  cerebrum,  or  the  lower  part  of  the  great  transverse  fissure. 
By  the  withdrawal  of  the  choroid  plexus,  it  is  converted  into 
an  artificial  gap  which  leads  directly  from  the  exterior  of  the 
brain  into  the  interior  of  the  descending  horn  of  the  lateral 
ventricle  (Fig.  189). 

Choroid  Plexus.  —  The  choroid  plexus  is  a  system  of 
convoluted  blood-vessels  in  connexion  with  a  fold  of  pia 
mater  which  is  prolonged  into  the  descending  horn  of  the 
lateral  ventricle  through  the  choroid  fissure  of  the  cerebrum. 
It  lies  on  the  surface  of  the  hippocampus  major,  and  is  con- 
tinuous behind  the  posterior  border  of  the  optic  thalamus  with 
the  choroid  plexus  in  the  body  of  the  lateral  ventricle.  But  it 
must  not  be  supposed  that  the  choroid  plexus  lies  free  in  the 
ventricular  cavity.  It  is  clothed  in  the  most  intimate  manner 
by  an  epithelial  layer,  which  represents  the  inner  or  mesial 
wall  of  the  descending  horn  pushed  into  the  cavity  by  the  choroid 
plexus.  The  ventricle,  therefore,  only  opens  on  the  surface 
through  the  choroid  cerebral  fissure  when  this  thin  epithelial 
layer  is  torn  away  by  the  withdrawal  of  the  choroid  plexus. 

Eminentia  Collateralis. — This  eminence  may  present  two 
distinct  forms,  which  may  be  distinguished  from  each  other 
as  the  eminentia  collateralis  posterior  and  the  eminentia  col- 
lateralis anterior. 

The  posterior  collateral  eminence  is  a  smooth  elevation  in 
the  floor  of  the  trigonum  ventriculi,  in  the  interval  between 
the  calcar  avis  and  the  hippocampus  major  as  they  diverge 
from  each  other.  The  anterior  collateral  eminence  is  not 
always  present.  It  forms  an  elongated  elevation  on  the  floor 
of  the  descending  horn  of  the  lateral  ventricle,  on  the  outer 
side  of  the  hippocampus  major.  Both  eminences  correspond 
to  the  collateral  fissure  on  the  inferior  aspect  of  the  cerebral 
hemisphere. 


THE  CEREBRUM  497 

Dissection. — The  remains  of  the  right  temporal  lobe  and  of  the  right 
occipital  lobe  should  now  be  detached  from  the  cerebrum  by  cutting 
through  the  fimbria  where  it  passes  into  the  posterior  pillar  of  the  fornix 
and  the  forceps  major  of  the  splenium  of  the  corpus  callosum.  The  knife 
should  then  be  carried  forwards  from  the  anterior  extremity  of  the 
descending  horn  above  the  level  of  the  uncus  through  the  temporal  pole. 
The  temporal  lobe,  with  the  hippocampal  convolution  along  its  inner  side, 
can  then  be  separated  from  the  remainder  of  the  brain,  along  the  line  of 
the  choroid  fissure  of  the  cerebrum.  In  the  detached  part  of  the  cerebrum 
(Fig.  189)  a  good  view  is  obtained  of  the  floor  of  the  descending  horn  and 
of  the  parts  in  relation  to  it.  Further,  by  replacing  it  in  position,  the 
choroid  cerebral  fissure  can  be  better  understood,  and  by  turning  the  brain 
upside  down  a  view  of  the  roof  of  the  descending  horn  and  the  structures 
in  relation  to  it  is  gained.  In  this  way  the  tail  of  the  caudate  nucleus  and 
the  taenia  semicircularis  can  be  traced  into  the  amygdaloid  nucleus. 

The  cut  edge  of  the  central  part  of  the  corpus  callosum,  which  is  still  in 
position,  should  now  be  still  farther  pared  away,  so  as  to  bring  more  fully 
into  view  the  subjacent  septum  lucidum  and  the  fornix. 


Septum  Lucidum — Fornix — Velum  Interpositum. 

Septum  Lucidum  (septum  pellucidum). — This  is  a  thin 
vertical  partition  which  intervenes  between  the  anterior  cornua 
and  the  fore-parts  of  the  bodies  of  the  two  lateral  ventricles 
(Fig.  183).  It  is  triangular  in  shape,  and  posteriorly  it  is 
prolonged  backwards  in  the  narrow  interval  between  the  body 
of  the  corpus  callosum  and  the  fornix,  to  both  of  which  it  is 
attached  by  its  upper  and  lower  edges.  In  front,  it  occupies 
the  gap  behind  the  genu  of  the  corpus  callosum  ;  whilst  below, 
in  the  narrow  interval  between  the  rostrum  of  the  corpus 
callosum  and  the  fornix,  it  is  prolonged  downwards  to  the 
base  of  the  brain. 

The  septum  lucidum  is  composed  of  two  thin  laminae  in 
apposition  with  each  other  in  the  mesial  plane.  The  mesial 
cleft  between  the  layers  is  termed  the  fifth  vetitricle  (Figs.  183 
and  185). 

Dissection. — The  narrow  middle  strip  of  the  corpus  callosum,  behind 
the  bend  of  the  genu,  should  now  be  removed.  Cut  it  transversely  across 
behind  the  genu,  and,  gently  raising  it,  separate  the  upper  edge  of  the 
septum  lucidum  from  its  lower  surface.  Farther  back,  behind  the  septum 
lucidum,  it  will  be  found  to  lie  upon  and  to  be  anatomically  connected  with 
the  upper  surface  of  the  fornix.  This  connexion  must  also  be  severed. 
The  left  forceps  major  should  be  preserved,  so  that  its  connexion  with  the 
occipital  lobe  may  be  more  fully  made  out  at  a  later  stage.  By  snipping 
off  the  upper  edge  of  the  septum  lucidum  with  the  scissors,  the  two  laminae, 
with  the  interposed  cleft  or  fifth  ventricle,  will  be  exposed. 

Fifth  Ventricle. — This  is  the   name  which  is  applied  to 
the    mesial    cleft    between    the    two    laminae    of   the    septum 
VOL.  11     3ii 


498  THE  BRAIN 

lucidum.  It  varies  greatly  in  extent  in  different  brains  and 
contains  a  little  fluid.  It  is  completely  isolated,  and  presents 
no  communication  with  the  other  ventricles  or  with  the 
surface.  Indeed,  the  term  "  ventricle "  is  somewhat  in- 
appropriate, because  its  developmental  history  shows  that  it 
has  nothing  in  common  with  the  general  ventricular  system 
of  the  brain. 

Fornix. — The  fornix  is  an  arched  bilateral  structure,  com- 
posed of  longitudinally  directed  fibres.  In  its  intermediate 
part,  its  two  lateral  halves  are  joined  together  in  the  mesial 
plane,  and  form  what  is  called  the  body  of  the  fornix ;  but  in 
front  and  behind  they  are  quite  separate,  and  constitute  the 
anterior  and  posterior  pillars  of  the  fornix. 

The  body  of  the  fornix  is  triangular  in  shape.  In  front, 
where  it  is  continuous  with  the  anterior  pillars,  it  is  narrow ; 
whilst  behind,  it  broadens  out,  becomes  flattened,  and  is  pro- 
longed into  the  posterior  pillars.  The  upper  surface  of  the 
body  of  the  fornix  is  in  contact  with  the  under  surface  of  the 
corpus  callosum,  and  in  the  mesial  plane  is  adherent  to  it, 
and  also  to  the  posterior  part  of  the  lower  edge  of  the  septum 
lucidum.  Beyond  these  attachments  on  each  side,  the  upper 
surface  of  the  body  of  the  fornix  forms  a  part  of  the  floor  of 
the  lateral  ventricle,  and  is  clothed  by  ependyma.  It  presents 
a  sharp  lateral  edge,  from  under  which  the  choroid  plexus  pro- 
jects into  the  cavity  of  the  lateral  ventricle,  and  with  which 
the  epithelial  layer  which  covers  that  plexus  is  continuous. 
The  lower  surface  of  the  body  of  the  fornix  rests  upon  the 
velum  interpositum,  a  fold  of  pia  mater,  which  separates  it 
from  the  third  ventricle  and  the  two  optic  thalami. 

The  anterior  pillars  of  the  fornix  (columnar  fornicis)  are 
two  rounded  strands  which  emerge  from  the  anterior  part  of 
the  body  of  the  fornix,  and  then  diverge  very  slightly  from 
each  other  as  they  curve  downwards  in  front  of  the  foramen 
of  Monro.  Sinking  into  the  grey  matter  on  the  lateral  wall 
of  the  third  ventricle,  each  anterior  pillar  proceeds  downwards 
to  the  base  of  the  brain,  where  it  protrudes  in  the  interpedun- 
cular space  to  take  part  in  the  formation  of  the  corpus 
mammillare. 

The  corpus  mammillare  has  the  appearance  of  being  a  twisted  loop  of 
the  anterior  pillar  of  the  fornix,  in  which  the  pillar  turns  upon  itself,  and 
is  then  continued  upwards  and  backwards  into  the  anterior  tubercle  of  the 
optic  thalamus.  This  appearance,  however,  is  deceptive.  In  the  interior 
of  the  corpus  mammillare  there  is  a  nucleus  of  grey  matter.      In  this  the 


^ORAMEN  OF 
MONRO 


THE  CEREBRUM  499 

fibres  of  the  anterior  pillar  end  ;  while  the  other  fibres  which  seem  to  be 
continuous  with  the  fornix  fibres  take  origin  within  the  nucleus.  The 
strand  thus  formed  is  called  the  bundle  of  Vicq  d1  Azyr. 

The  connexions  which  have  just  been  described  cannot  be  made  out  at 
present,  but  at  a  later  period  the  dissector  will  experience  little  difficulty 
in  tracing  the  anterior  pillar  of  the  fornix  to  the  corpus  mammillare,  and 
in  displaying  the  connexion  of  this  with  the  bundle  of  Vicq  d'Azyr. 

The  posterior  pillars  of  the  fornix  are  flattened  bands  which 
diverge  widely  from  the  body  of  the  fornix.  At  first  they  are 
adherent  to  the  under  surface  of 

tSODV 

the  corpus  callosum,  but  soon 
they  sweep  downwards  round  the 
posterior     ends     of     the      optic     „. . ,   'IV    //■■  II 6UNDU  0f 

r  r  ant"  pillar  \  \    // 

thalami,  and  enter  the  posterior 
horns  of  the  lateral  ventricles. 
Here  each  posterior  pillar  comes 
into  relation  with  the  correspond-        FlG   I9a_Diagram  of  the 

ing    hippocampus    major,     and     a  Fornix;   profile  view. 

portion  of  its  fibres  become  spread 

out  on  the  surface  of  this  prominence,  forming  the  alveus, 
whilst  the  remainder  constitute  the  fimbria,  which  has  already 
been  described  (pp.  482,  495). 

Dissection. — The  body  of  the  fornix  should  now  be  divided  transversely 
across  its  middle.  Its  posterior  and  anterior  portions  may  then  be  gently 
raised  from  the  velum  interpositum,  and  thrown  forwards  and  backwards. 
Had  it  been  possible  to  raise  the  corpus  callosum  and  fornix  together,  the 
diverging  posterior  pillars  of  the  latter  would  have  been  seen  to  limit  a 
triangular  space  on  the  under  surface  of  the  corpus  callosum  in  front  of  the 
posterior  margin  of  the  splenium.  This  interval  is  termed  the  lyra,  and  is 
traversed  by  a  series  of  oblique  and  longitudinal  markings.  These  mark- 
ings indicate  the  presence  of  fibres,  which  pass  across  from  one  pillar  of 
the  fornix  to  the  other,  so  as  to  form  a  white  lamina.  This  lamina  is  not 
united  to  the  under  surface  of  the  corpus  callosum,  and  the  interval  between 
them  is  sometimes  termed  Vergcts  ventricle. 

Velum  Interpositum.  This  lamina  is  formed  by  a  double 
layer  or  fold  of  pia  mater  which  intervenes  between  the  body 
of  the  fornix,  which  is  placed  above  it,  and  the  roof  of  the 
third  ventricle  and  the  two  optic  thalami,  which  lie  below  it. 
Between  the  two  layers  are  blood  vessels  and  some  subarach- 
noidal trabecular  tissue.  In  shape  the  velum  interpositum  is 
triangular,  and  the  narrow  anterior  end  or  apex  reaches  as  far 
forwards  as  the  foramina  of  Monro.  The  base  lies  under  the 
splenium  of  the  corpus  callosum,  and  here  the  two  layers  of 
pia  mater  which  form  the  velum  become  continuous  with  the 
investing  pia  mater  on  the  surface  of  the  brain. 

[i— 32  a 


5°° 


THE   BRAIN 


Along  each  lateral  margin  the  velum  interpositum  is 
bordered  by  the  choroid  plexus  of  the  body  of  the  lateral 
ventricle,  which  projects  into  the  ventricular  cavity  from 
under  cover  of  the  lateral  free  edge  of  the  fornix.  Posteriorly, 
this  choroid  plexus  is  continuous  with  the  similar  structure  in 
the  descending  horn  of  the  ventricle  ;  whilst  in  front,  it  narrows 
greatly,  and  becomes  continuous,  across  the  mesial  plane,  with 


Ventricle  v. 


Fornix  divided 


Vein  of 
corpus  striatum 


Taenia 
semicircularis 


Vein  of  Galen 
Posterior  pillar  of  fornix- 


Genu  of  corpus  callosum 


V.   Septum  lucidum 


!«^.-    Caudate  nucleus 

1 
i  i/      Anterior  pillar 

V4--  of  fornix 


Velum 
interpositum 


Choroid  plexus 
Lyra 


■•.  Body  of  fornix 
thrown  hack 


Fig.  191. — Dissection  to  show  Velum  Interpositum  and  the  parts  in  its 
vicinity.      The  fornix  has  been  divided  and  thrown  back. 


the  corresponding  plexus  of  the  opposite  side,  behind  the 
epithelium  which  lines  the  foramina  of  Monro.  From  this 
median  junction  two  much  smaller  choroid  plexuses  run  back- 
wards on  the  under  surface  of  the  velum  interpositum,  and 
project  downwards  into  the  third  ventricle.  These  are  the 
choroid  plexuses  of  the  third  ve?itricle  (Fig.  192). 

The  most  conspicuous  blood  vessels  in  the  velum  inter- 
positum are  the  two  veins  of  Galen,  which  run  backwards — 
one  on  either  side  of  the  mesial  plane.  In  front,  each  is 
formed  at  the  apex  of  the  fold  by  the  union  of  the  vein  of  the 


THE  CEREBRUM 


5QI 


corpus  striatum  with  a  large  vein  issuing  from  the  choroid 
plexus ;  behind,  they  unite  to  form  the  vena  magna  Galeni, 
and  this  pours  its  blood  into  the  anterior  end  of  the  straight 
sinus. 

Transverse  Fissure. — This  name  is  given  to  the  continuous 
cleft  through  which  the  velum  interpositum  and  the  choroid 
plexuses  of  the  two  descending  horns  of  the  lateral  ventricles 
are  introduced  into  the  interior  of  the  brain.  It  consists  of 
an  upper  or  intermediate  part   and  two  lateral  parts.      The 


TAENIA/ 
SEMICIRC 


VELUM 
INTERPOSITUM 


CHOROID  PLEXUS 
VENT  III 


FlG.  192.  —  Diagrammatic  coronal  section  through  the  Optic  Thalami  and 
the  parts  in  immediate  relation  to  them.  The  intermediate  part  of 
the  great  transverse  fissure  holding  the  velum  interpositum  is  seen, 
and  also  the  manner  in  which  this  fissure  is  shut  out  from  the  lateral 
ventricles  by  the  epithelium  which  covers  the  choroid  plexus  on 
each  side. 


former  passes  forwards  between  the  splenium  of  the  corpus 
callosum  and  the  body  of  the  fornix  above,  and  the  roof  of 
the  third  ventricle  and  the  optic  thalami  below.  It  is  limited 
by  the  epithelial  covering  of  the  choroid  plexuses,  which  shuts 
out  these  structures  from  the  cavity  of  the  lateral  ventricles. 

The  lateral  part  of  the  transverse  fissure  is  termed  the 
choroidal  fissure.  It  is  continuous  with  the  intermediate  part, 
and  has  already  been  studied  in  connexion  with  the  descend- 
ing horn  of  the  lateral  ventricle  (p.  49C)). 

Dissection.  The  vein  of  the  corpus  striatum  should  now  be  divided  on 
each  side   as   it   passes  into   the  vein  of  Galen.      The  apex  of  the  velum 


5Q2  THE  BRAIN 

inlerpositum  should  then  be  seized  with  the  forceps,  and  the  whole 
structure  pulled  backwards.  The  entire  upper  surface  of  the  optic 
thalamus  on  each  side  is  thus  exposed,  and  between  these  bodies  is  seen 
the  mesially  placed  third  ventricle.  The  roof  of  this  ventricle,  which  is 
epithelial  and  invaginated  into  the  cavity  by  the  choroid  plexuses  on  the 
under  surface  of  the  velum  interpositum,  is  torn  away  with  that  structure. 
The  basal  part  of  the  velum  interpositum  is  intimately  connected  with  the 
pineal  body  which  lies  on  the  mesencephalon  behind  the  third  ventricle. 
Care  therefore  must  be  taken  to  extricate  this  body  from  the  pia  mater, 
otherwise  it  is  sure  to  be  pulled  away. 


The  Optic  Thalami  and  the  Third  Ventricle. 

Optic  Thalamus. — The  optic  thalamus  is  a  large  ovoid 
mass  of  grey  matter  which  lies  obliquely  across  the  path  of 
the  crus  cerebri  as  it  ascends  into  the  cerebrum.  The 
smaller  anterior  end  of  the  thalamus  lies  close  to  the  mesial 
plane,  and  is  only  separated  from  the  corresponding  part  of 
the  opposite  side  by  a  very  narrow  interval.  The  enlarged 
posterior  ends  of  the  two  thalami  are  placed  more  widely 
apart ;  and  in  the  interval  between,  the  corpora  quadrigemina 
are  situated.  In  their  anterior  two-thirds,  the  two  thalami  lie 
close  together,  and  a  deep  mesial  cleft,  the  third  ventricle  of 
the  brain,  intervenes  between  them.  Each  thalamus  presents 
an  anterior  and  a  posterior  extremity,  and  four  surfaces. 
The  inferior  and  external  surfaces  are  in  apposition,  and, 
indeed,  directly  connected  with  adjacent  parts,  and  on  this 
account  it  is  only  possible  to  study  them  by  means  of  sections 
through  the  brain.  The  superior  and  internal  surfaces  are 
free,  and  may  be  examined  in  the  present  dissection. 

The  external  or  lateral  surface  of  the  optic  thalamus  is 
applied  to  a  mass  of  white  matter,  termed  the  internal  capsule, 
which  is  largely  composed  of  fibres  derived  from  the  crusta  or 
ventral  part  of  the  crus  cerebri.  The  inferior  or  ventral 
surface  of  the  thalamus  rests  chiefly  upon  the  subthalamic 
region  or  the  prolongation  upwards  of  the  dorsal  tegmental 
part  of  the  crus  cerebri.  The  relation,  therefore,  which  this 
body  presents  to  the  upward  continuation  of  the  crus  cerebri 
is  very  intimate. 

The  superior  or  dorsal  surface  of  the  thalamus  is  free. 
On  the  outer  side  it  is  bounded  by  the  groove,  already 
noticed,  on  the  floor  of  the  lateral  ventricle  which  intervenes 
between  the  thalamus  and  the  caudate  nucleus — a  groove 
which  contains  the  vein  of  the  corpus  striatum  and  the  taenia 


THE  CEREBRUM 


5°3 


semicircularis.  On  the  inner  side  the  superior  surface  of  the 
thalamus  is  separated  in  its  anterior  half  from  the  internal 
or  mesial  surface  by  a  sharp  edge,  or  prominent  ledge,  of  the 
ependyma  of  the  third  ventricle.  This  is  called  the  tenia 
thalami,  and  the  ridge  which  it  forms  is  accentuated  by  the  fact 
that  subjacent  to  it  there  lies  a  longitudinal  strand  of  fibres 
called  the  stria  medullaris.     When  these  two  structures,  viz.. 


Cut  surface  of  genu 
of  corpus  callosum 


Genu  of  corpus  callosum 


Ventricle  v. ■  — 


Fornix 

Anterior  commissure 

Middle  commissure — 


Groove  on  thalamus 
for  fornix 


Posterior  commissure -- 

Trochlear  nerve 
Middle  peduncle  of 
cerebellum 
Corpora  quadrigemina 


Superior  cerebellar  peduncle 


-  Septum  lucidum 
~  Caudate  nucleus 

-  •  Anterior  pillar  of  fornix 

Anterior  tubercle  of 
optic  thalamus 

I . .  Vein  of  corpus 
striatum 

;.~  Ventricle  m. 
Taenia  thalami 

"  Trigonum  habenula.- 

'Puhinar 

Stalk  of  pineal  body- 
Pineal  body 


Lingula  of  cerebellum 


FlG.   193. — The  two  Optic  Thalami  and  the  Third  Ventricle 
as  seen  from  above. 


the  ependyma!  ridge  and  the  subjacent  tract,  are  traced  bark- 
wards,  they  are  seen  to  turn  inwards  and  become  continuous 
with  the  stalk  of  the  pineal  body.  Between  the  hinder  part 
of  the  taenia  thalami  and  the  thalamus  there  is  a  small 
depressed  triangular  area,  the  trigonum  habenulce,  situated  in 
front  of  the  superior  quadrigeminal  body. 

The  superior  surface  of  the  thalamus  is  slightly  bulging  or 
convex,  and  is  of  a  whitish  colour  owing  to  the  presence  of  a 


5°4 


THE   BRAIN 


thin  superficial  coating  of  nerve  fibres  (stratum  zonale).  It 
is  divided  into  two  areas  by  a  faint  oblique  groove  which 
begins  in  front  a  short  distance  behind  the  anterior  extremity 
of  the  thalamus,  and  extends  obliquely  outwards  and  back- 
wards. This  sulcus  corresponds  to  the  free  outer  edge  of  the 
fornix.  The  two  areas  thus  mapped  out  are  very  differently 
related  to  the  ventricles  of  the  brain.  The  outer  area 
includes  the  anterior  extremity  of  the  thalamus,  and  forms  a 
part  of  the  floor  of  the  lateral  ventricle ;  it  is  covered  with 
ependyma,  and  overlapped  by  the  choroid  plexus  (Fig.  192). 
The  inner  area  intervenes  between  the  lateral  and  third 
ventricles  of  the  brain,  and  takes  no  part  in  the  formation  of 
the  walls  of  either.  It  is  covered  by  the  velum  interpositum, 
above  which  is  the  fornix.  It  includes  the  posterior  extremity 
of  the  thalamus. 

The  anterior  extremity  of  the  thalamus,  called  the  anterior 
tubercle  (tuberculum  anterius),  is  rounded  and  prominent. 
It  projects  into  the  lateral  ventricle,  lies  behind  and  to  the 
outer  side  of  the  free  portion  of  the  anterior  pillar  of  the 
fornix,  and  bounds  the  foramen  of  Monro  behind. 

The  posterior  extremity  of  the  thalamus  is  very  prominent, 
and  projects  backwards  so  as  to  overhang  a  portion  of  the 
mesencephalon  (viz.,  the  brachia  of  the  quadrigeminal  bodies) 
(Fig.  193).  This  projecting  part  is  called  the  pulvinar. 
But  the  hinder  end  of  the  thalamus  shows  another  prominence. 
This  is  situated  below  and  to  the  outer  side  of  the  pulvinar. 
It  is  oval  in  form,  and  receives  the  name  of  the  corpus 
geniculatum  externum. 

The  mesial  surfaces  of  the  two  thalami  are  placed  very 
close  together,  and  are  covered  not  only  by  the  lining 
ependyma  of  the  third  ventricle,  but  also  by  a  tolerably  thick 
layer  of  grey  matter  continuous  below  with  the  grey  matter 
which  surrounds  the  aqueduct  of  Sylvius  in  the  mesen- 
cephalon. A  band  of  grey  matter,  termed  the  grey  or  soft 
commissure  of  the  brain  (commissura  mollis),  crosses  the  third 
ventricle  and  joins  the  two  thalami  together. 

Pineal  Body  (corpus  pineale). — This  is  a  small  body  of  a 
darkish  colour,  and  about  the  size  of  a  cherry-stone,  which 
is  placed  between  the  hinder  extremities  of  the  two  thalami 
on  the  dorsal  aspect  of  the  mesencephalon  (Fig.  193).  It 
occupies  the  depression  between  the  two  superior  quadri- 
geminal bodies,  and  is  shaped  like  a  fir-cone.      Its  base,  which 


THE  CEREBRUM  505 

is  directed  upwards,  is  attached  by  means  of  a  hollow  stalk  or 
peduncle.  This  stalk  is  separated  into  a  dorsal  and  a  ventral 
part  by  a  continuation  backwards  into  it  of  a  pointed  recess 
of  the  cavity  of  the  third  ventricle.  The  dorsal  part  of  the 
stalk  is  carried  forwards  on  each  optic  thalamus  as  the  taenia 
thalami ;  the  ventral  part  is  folded  round  a  narrow  but  con- 
spicuous cord-like  band  of  white  fibres,  which  crosses  the 
mesial  plane  immediately  above  the  base  of  the  pineal  body, 
and  receives  the  name  of  the  posterior  commissure  of  the 
cerebrum. 

Anterior  Commissure  of  the  Cerebrum. — In  the  anterior 
part  of  the  cleft  between  the  two  optic  thalami,  and  immedi- 
ately in  front  of  the  anterior  pillars  of  the  fornix,  a  round 
bundle  of  white  fibres  will  be  seen  crossing  the  mesial  plane. 
This  is  the  anterior  commissure.  It  is  very  much  larger  than 
the  posterior  commissure,  and  will  be  afterwards  followed 
towards  the  temporal  lobe  in  which  the  greater  part  of  it  ends. 

Third  Ventricle. — This  name  is  given  to  the  deep  narrow 
cleft  between  the  two  optic  thalami.  Its  depth  rapidly  in- 
creases from  behind  forwards,  and  it  may  be  considered  to 
extend  from  the  pineal  body  behind  to  the  anterior  commis- 
sure and  lamina  cinerea  in  front.  Its  floor  is  formed  by  the 
parts  already  studied  within  the  interpeduncular  space  on  the 
base  of  the  brain,  viz.,  the  tuber  cinereum,  the  corpora  mam- 
millaria,  and  the  grey  matter  of  the  locus  perforatus  posticus, 
and  also  to  some  extent  behind  these  by  the  tegmenta  of  the 
crura  cerebri.  In  front,  it  is  bounded  by  the  lamina  cinerea 
and  the  anterior  commissure ;  whilst  its  lateral  walls  are 
formed  by  the  mesial  surfaces  of  the  two  optic  thalami.  A 
little  in  front  of  the  middle  of  the  ventricle  the  cavity  is 
crossed  by  the  middle  or  soft  commissure,  which  connects  the 
thalami  with  each  other,  and  in  front  of  this  the  anterior 
pillar  of  the  fornix  is  seen  descending  in  the  lateral  wall.  At 
first  this  is  distinct  and  prominent,  but  it  gradually  becomes 
more  and  more  sunk  in  the  grey  matter  on  the  side  of  the  ven- 
tricle as  it  approaches  the  corresponding  corpus  mammillare. 

The  roof 'of  the  third  ventricle  is  formed  by  a  thin  epithelial 
layer  continuous  with  the  epithelial  lining  of  the  cavity,  which 
stretches  across  the  mesial  plane  from  the  one  taenia  thalami 
to  the  other.  It  is  applied  to  the  under  surface  of  the  velum 
interpositum  which  overlies  the  ventricle,  and  is  invaginated 
into  the   cavity  by  the   choroid   plexuses  which    hang  down 


506 


THE  BRAIN 


from  the  under  surface  of  this  fold  of  pia  mater.  In  the 
removal  of  the  velum  interpositum  this  thin  epithelial  roof 
has  been  torn  away. 

The  third  ventricle  communicates  freely  with  the  lateral 
ventricles,  and  also  with  the  fourth  ventricle.  The  aqueduct 
of  Sylvius,  a  narrow  channel  which  tunnels  the  mesencephalon, 
brings  it  into  communication  with  the  fourth  ventricle.  The 
opening  of  this  aqueduct  will  be  seen  at  the  posterior  part 
of  the  floor  of  the  ventricle,  immediately  below  the  posterior 


Sulcus  of  Monro 

Choroid  plexus 
Anterior  pillar 
of  fornix 


Foramen  of  Monro 
Septum  lucidum 

Genu 


Corpus  callosum 

i  Middle  commissure 

i  ■     Optic  thalamus 

■      .'    Taenia  thalami 
'      ,'      '       Mesencephalon 

'     Pineal  body 


/  Quadrigeminal  bodies 
Splenium 

Aqueduct  of  Sylvius 
.    Culnien  monticuli 


Anterior  .  - ' 
commissure  ..-■"' 

Corpus  mammillare'         .  - 
Lamina  cinerea  ' 

Optic  nerve  ' 
Pituitary  body 

Tuber  cinereum     • 

Third  nerve       ,' 

Pons        / 
Valve  of  Vieussens 
Ventricle  iv, 

Medulla  .' 
Choroid  plexus 
in  Ventricle  IV. 


Clivus  monticuli 


'"-.    Folium 
cacuminis 

Tuber  valvule 


Pyramid 


Uvula 
Central  lobule 


Nodule 


Fig.  194. — Mesial  section  through  the  Corpus  Callosum,  Third  Ventricle, 
Mesencephalon,  Pons,  Cerebellum,  and  Medulla. 


commissure.  The  foramina  of  Monro  bring  it  into  communi- 
cation with  the  two  lateral  ventricles.  The  latter  apertures 
are  placed  at  the  upper  and: fore  parts  of  the  lateral  walls, 
and  lead  outwards  and  slightly  upwards  between  the  most 
prominent  parts  of  the  anterior  pillars  of  the  fornix,  and 
the  anterior  tubercles  of  the  optic  thalami.  They  are  just 
large  enough  to  admit  a  crow-quill,  and  through  these  pas- 
sages the  epithelial  lining  of  the  three  ventricles  becomes 
continuous. 

From  the  foramen  of  Monro  a  distinct  groove  on  the  lateral 


THE  CEREBRUM  507 

wall  of  the  ventricle  leads  backwards  towards  the  mouth  of 
the  Sylvian  aqueduct.      It  is  termed  the  sulcus  of  Monro. 

The  outline  of  the  third  ventricle,  when  viewed  from  the  side  in  a 
mesial  section  through  the  brain  (Fig.  184),  or  as  it  is  exhibited  in  a  plaster 
cast  of  the  ventricular  system  of  the  brain,  is  seen  to  be  very  irregular. 
It  presents  several  diverticula  or  recesses.  Thus,  in  the  fore-part  of  the 
floor  there  is  a  deep  funnel-shaped  pit  or  recess  leading  down  through  the 
tuber  cinereum  into  the  infundibulum  of  the  pituitary  body.  Another 
recess  leads  forwards  immediately  in  front  of  this,  above  the  optic  chiasma. 
Posteriorly,  two  additional  recesses  are  present.  One,  the  recessus pinealis, 
passes  backwards,  above  the  posterior  commissure  and  the  entrance  of  the 
aqueduct  of  Sylvius,  for  a  short  distance  into  the  stalk  of  the  pineal  body. 
The  second  is  placed  above  this,  and  is  carried  backwards  for  a  greater 
distance.  Its  walls  are  epithelial,  and  therefore  it  cannot  be  seen  in  an 
ordinary  dissection.      It  is  termed  the  recessus  suprapinealis. 

Dissection. — The  further  study  of  the  cerebrum  should  be  postponed 
until    after  the   examination  of  the   mid-brain    or    mesencephalon.     The 


FORAMEN    OF    MONRO. 


\recessus 

OPTIC  CmASMA^^  C\>SUPRAPINEALlS 

^RECESSUS  PINEALIS 
\^\  POSTR.  COM. 

AQUEDUCT  OF  SVLVIUS 


PITUITARY  BODY 


Fig.  195. — Diagrammatic  outline  of  the  Third  Ventricle 
as  viewed  from  the  side. 

membranes  should  be  removed  from  the  upper  surface  of  the  cerebellum, 
and  the  prominent  anterior  part  of  this  organ  may  then  be  gently  pulled 
backwards  to  expose  as  far  as  possible  the  corpora  quadrigemina,  i.e. ,  the 
four  rounded  eminences  on  the  dorsal  aspect  of  the  mesencephalon.  In 
doing  this,  care  should  be  taken  to  secure  and  preserve  the  slender  trochlear 
nerve  which  winds  forwards  round  the  outer  side  of  the  crus  cerebri,  and 
which  issues  from  a  lamina  called  the  valve  of  Vieussens,  immediately 
below  the  inferior  pair  of  quadrigeminal  bodies. 


THE  MESENCEPHALON. 

The  mesencephalon  is  the  stalk  which  occupies  the  opening 
of  the  tentorium  cerebelli,  and  connects  the  cerebrum  with 
the  parts  in  the  posterior  cranial  fossa.  It  is  about  three- 
quarters  of  an  inch  long,  and  it  consists  of  a  dorsal  part, 
composed  of  the  corpora  quadrigemina,  and  a  much  larger 


508  THE  BRAIN 

ventral  part,  which  is  formed  by  the  two  large  crura  cerebri. 
In  the  undissected  brain  the  corpora  quadrigemina  are  com- 
pletely hidden  from  view  by  the  splenium  of  the  corpus 
callosum,  which  projects  backwards  over  them,  and  also  by 
the  superimposed  cerebral  hemispheres.  The  crura  cerebri, 
however,  can  to  some  extent  be  seen  on  the  base  of  the  brain, 
where  they  bound  the  posterior  part  of  the  interpeduncular 
space.  The  mesencephalon  is  tunnelled  from  below  upwards 
by  a  narrow  passage  called  the  aqueduct  of  Sylvius.  This 
channel  lies  much  nearer  its  dorsal  than  its  ventral  surface. 

Corpora  Quadrigemina  (optic  lobes). — The  four  rounded 
eminences  on  the  dorsal  aspect  of  the  mesencephalon  to 
which  this  name  is  applied  are  for  the  most  part  composed  of 
grey  matter,  although  each  has  a  superficial  coating  of  white 
fibres.  The  superior  pair  are  larger  and  broader  than  the 
inferior  pair,  but  they  are  not  so  well  denned  nor  yet  so 
prominent. 

A  longitudinal  and  a  transverse  groove  separate  the  quadri- 
geminal  bodies  from  each  other.  The  longitudinal  groove 
occupies  the  mesial  plane,  and  extends  upwards  as  far  as  the 
posterior  commissure.  From  its  lower  end  a  short  but  well- 
defined  narrow  band  of  white  fibres,  the  frenulum  veli,  passes 
to  the  valve  of  Vieussens — a  lamina  placed  immediately 
below  the  inferior  pair  of  quadrigeminal  prominences.  The 
upper  part  of  the  longitudinal  groove  is  occupied  by  the 
pineal  body.  The  Iransverse  groove  curves  round  behind  each 
of  the  superior  pair  of  quadrigeminal  bodies,  and  separates 
them  from  the  inferior  pair. 

Brachia  of  the  Corpora  Quadrigemina. — The  corpora 
quadrigemina  are  not  marked  off  from  the  side  of  the  mesen- 
cephalon, but  each  body  has  in  connexion  with  it  on  this 
aspect  a  prominent  white  strand,  which  is  prolonged  upwards 
and  forwards  under  the  projecting  pulvinar  and  corpus  genicu- 
latum  externum  on  the  hinder  end  of  the  optic  thalamus. 
These  strands  are  called  the  brachia  of  the  corpora  quadri- 
gemina, and  they  are  separated  from  each  other  by  a  continu- 
ation on  the  side  of  the  mesencephalon  of  the  transverse 
groove  which  intervenes  between  the  two  pairs  of  bodies. 

Corpus  G-eniculatum  Internum. — Closely  connected  with 
the  brachia  of  the  corpora  quadrigemina  will  be  seen  the 
corpus  geniculatum  internum.  It  is  a  little  oval  eminence, 
very  sharply  defined,  which  lies  on  the  side  of  the  upper  part 


THE   MESENCEPHALON  509 

of  the  mesencephalon  under  shelter  of  the  pulvinar  of  the 
optic  thalamus. 

Connexions  of  the  Brachia  and  the  Origin  of  the  Optic 
Tract. — It  will  now  be  seen  that  the  brachia  are  intimately 
connected  with  the  optic  tract.  The  inferior  brachium  pro- 
ceeding upwards  from  the  lower  quadrigeminal  body  advances 
towards  the  corpus  geniculatum  internum,  and  disappears 
from  view  under  cover  of  this  prominence.  Upon  the 
opposite  side  of  this  same  geniculate  body,  the  mesial  root 
of  origin  of  the  optic  tract  is  observed  to  arise,  and  the 
appearance  is  such  that  the  dissector  might  very  naturally 
conclude  that  the  inferior  brachium  and  this1  root  of  the 
optic  tract  are  continuous.  This,  however,  is  not  the  case. 
The  superior  brachium  is  carried  upwards  and  forwards  between 
the  overhanging  pulvinar  and  the 

D        O  i  PULVINAR 

corpus    geniculatum     internum.  ,corpgenext 

It  partly  enters  the  corpus  genicu- 
latum externum,  but  a  portion 
of    it    can    easily    be    observed 

to  be    directly    continuous   with    \^J  ^mesial root 

the  lateral  root  of  the  optic  tract.    /QKx  corpgenint: 


LATERAL  ROOT. 

OPTIC  TRACT 


SUPR.  BRACHIUM. 
INFR.  BRACHIUM. 
SUPR.  QUADBODY; 
INFR   QUAD  BODY. 


The  optic  tract  when   traced  back- 
wards  divides    into    a    mesial    and    a 
lateral   root.       The  mesial  root  enters 
the  corpus  geniculatum  internum.    The      FKJ.  196.— Diagram  of  the  Roots 
lateral  root  is  partly  continued  into  the  of  lhe  Optlc  Tract, 

superior  brachium,  whilst  the  remainder 

of  its  fibres  enter  the  corpus  geniculatum  externum  and  the  pulvinar. 
The  superior  quadrigeminal  body,  the  corpus  geniculatum  externum,  and 
the  pulvinar  constitute  the  lower  visual  centres. 

Crura  Cerebri. — The  crura  cerebri  constitute  the  chief 
bulk  of  the  mesencephalon.  When  viewed  from  below,  they 
appear  as  two  large  rope -like  strands,  which  emerge  close 
together  from  the  upper  aspect  of  the  pons  Varolii,  and 
diverge  as  they  proceed  upwards  to  enter  the  cerebrum.  At 
the  point  where  each  crus  disappears  into  the  corresponding 
side  of  the  hemisphere,  it  is  embraced  on  its  outer  side  by 
the  optic  tract. 

The  crus  cerebri  of  each  side  consists  of  two  parts,  viz.,  a 
dorsal  tegmentum,  which  is  prolonged  upwards  to  the  region 
below  the  thalamus;  and  a  ventral  crusta  or  pes,  which  is 
carried  upwards  into  the  internal  capsule  on  the  outer  side  of 
the  thalamus.      When    the   base   of  the   brain  is  examined,  it 


5to 


THE  BRAIN 


is  the  crusta  which  is  seen,  and  it  is  observed  to  be  white 
in  colour  and  streaked  in  the  longitudinal  direction.  On 
the  exterior  of  the  mesencephalon,  the  separation  between  the 
two  parts  of  the  crus  cerebri  (i.e.,  the  tegmentum  and  the 
crusta)  is  indicated  by  an  inner  and  an  outer  groove  or  sulcus. 
The  inner  or  mesial  sulcus  is  the  deeper  and  more  distinct. 
It  looks  into  the  interpeduncular  space,  and  from  it  emerge 
the  fascicles  of  the  oculo- motor  nerve.  It  consequently 
receives  the  name  of  the  sulcus  oculo?notorius.  The  outer 
sulcus  is  termed  the  sulcus  lateralis. 


Corpus  geniculatum  internum 
Pulvinar 


Taenia  semicircularis 


Corpus  geniculatum 


externum  n       \  \ 

1         \ 


Optic  tract 
Anterior  perforated  spot 


Superior  brachium 
Inferior  brachium 

Superior  quadrigeminal  body 

Inferior 
quadrigeminal  body 


Aqueduct  of  Sylvius 


Posterior  perforated 
spot 

—Corpus  albicans 
Tuber  cinereum 
Optic  commissure 


Optic  nerve 


Fig.  197. — The  Origin  and  Relations  of  the  Optic  Tract. 
(Professor  Thane,  from  Quairis  Anatomy.) 


Dissection. — The  mesencephalon  should  now  be  divided  transversely  by 
one  sweep  of  the  knife  at  the  level  of  the  lower  borders  of  the  superior  pair 
of  corpora  quadrigemina.  By  this  proceeding,  the  cerebrum  is  separated 
from  the  parts  below.  A  number  of  very  important  points  can  be  made 
out  on  the  cut  surface  of  the  mesencephalon. 

Cut  Surface  of  the  Mesencephalon  (Fig.  198). — Much 
nearer  the  dorsal  than  the  ventral  surface  of  the  mesencephalon 
the  transversely  divided  aqueduct  of  Sylvius  may  be  seen.  As 
already  stated,  this  narrow  passage  leads  from  the  fourth 
ventricle  below,  upwards  through  the  mesencephalon  to  the 
third  ventricle  above.  It  is  surrounded  by  a  thick  layer  of 
grey  matter,  called  the  Sylvian  grey  matter,  or  the  central 
grey  matter  of  the  aqueduct.  In  a  fresh  brain  this  is  always 
very  conspicuous,  and  in  its  midst  are  situated  the  nuclei  of 


THE  MESENCEPHALON 


511 


the  oculo-motor  and  trochlear  nerves,  and  the  upper  nucleus 
of  the  trigeminal  nerve,  although  of  course  these  cannot, 
except  in  very  favourable  circumstances,  be  detected  by  the 
naked  eye.  Below,  this  grey  matter  of  the  aqueduct  is  con- 
tinuous with  the  grey  matter  spread  out  on  the  floor  of  the 
fourth  ventricle ;  whilst  above,  it  is  continuous  with  the  grey 
matter  on  the  floor  and  sides  of  the  third  ventricle. 

The  division  between  the  tegmentum  and  the  crusta  is 
rendered  very  evident  by  a  conspicuous  mass  of  dark  pigmented 
matter  which  intervenes  between  them.  This  is  termed  the 
substantia  nigra. 

Substantia  Nigra. — As  seen  in  transverse  section,  the  sub- 


'SoRPORA  QUADR,GEM,N?VSYLV.ANtter 


POSTERIOR 
LONGITUDINAL    /         TEGMENT 
BUNDLE 


AQUEDUCT  OF  SYLViUS. 


SULCUS  LATERALIS 


OCULOMOTOR 
NERVE 


SULCUS    OCULOMOTORIUS 


Fig.  198. — Diagrammatic  view  of  the  Cut  Surface  of  the  Mesencephalon 
when  transversely  divided. 


stantia  nigra  presents  a  somewhat  crescentic  outline.  It  is 
composed  of  a  mass  of  grey  matter  in  the  midst  of  which  are 
large  numbers  of  pigmented  nerve  cells.  The  substantia 
nigra  is  in  reality  disposed  in  the  form  of  a  thick  band 
interposed  between  the  pedal  and  tegmental  parts  of  the 
cms  cerebri.  Below,  it  begins  at  the  upper  border  of  the 
pons  Varolii,  and  it  extends  upwards  into  the  subthalamic 
region.  The  margins  of  this  band  of  dark-coloured  substance 
come  to  the  surface  at  the  oculo-motor  and  lateral  sulci,  and 
its  inner  part  is  traversed  by  the  emerging  nerve  fibres  of  the 
oculo-motor  nerve.  The  surface  turned  towards  the  tegmentum 
is  concave  and  uniform ;  the  opposite  surface  is  convex,  and 
rendered  highly  irregular  by  the  presence  of  numerous  slender 
prolongations  of  the  substance  into  the  crusta. 


5'2 


THE  BRAIN 


Crusta. — The  crusta  is  somewhat  crescentic  when  seen  in 
section,  and  stands  quite  apart  from  its  fellow  of  the  opposite 
side.  It  is  composed  of  a  compact  mass  of  longitudinally 
directed  nerve  fibres  which  are  carried  upwards  into  the 
internal  capsule.  The  middle  third  or  more  of  each  crusta  is 
composed  of  the  important  pyramidal  tract  as  it  descends  from 
the  motor  area  of  the  cerebral  cortex,  but  this  is  quite  in- 
inferior  quadrigeminal  body 


Sylvian  grey  matter 


Sylvian  aqueduct— _C 


^Mesencephalic  root  of  fifth  nerve 

„  'Nucleus  of  fourth  nerve 
,  '  Inferior  brachium 
fc.^      ,  -  -  Posterior  longitudinal  bundle 

.Mesial  fillet 


/ 


Raphe 
Superior  cerebellar  peduncle 


Crusta 
Substantia  nigra 

Fig.  199. — Transverse  section  through  the  Mesencephalon  at  the  level  of  the 
inferior  quadrigeminal  body  :  right  side  only  reproduced.  The  drawing 
is  taken  from  a  YVeigert-Pal  specimen,  and  therefore  the  grey  matter  is 
pale  and  the  strands  of  white  matter  are  dark.  The  dark  colour  of  the 
substantia  nigra  is  not  evident  owing  to  the  thinness  of  the  section. 

distinguishable  from  the  portions  of  the  crusta  which  lie  on 
either  side  of  it. 

Tegmentum. — Unlike  the  crustae,  the  tegmenta  are  directly 
continuous  with  each  other  in  the  mesial  plane,  a  faint  line, 
termed  the  median  raphe,  alone  indicating  their  bilateral 
character.  Towards  the  dorsum  of  the  mesencephalon  they 
are  also  fused  with  the  bases  of  the  corpora  quadrigemina. 
Their  lateral  surfaces  therefore  are  alone  free. 


THE  MESENCEPHALON 


5i3 


The  tegmentum  is  composed  of  an  admixture  of  grey  and  white  matter, 
constituting  what  is  termed  the  formatio  reticularis.  The  white  matter  is 
composed  of  fibres  running  both  transversely  and  longitudinally.  Certain 
of  the  longitudinal  fibres  are  grouped  together  and  form  well-marked 
tracts,  which,  in  a  section  through  the  mesencephalon  of  a  fresh  brain,  can 
be  detected  by  the  naked  eye.  These  tracts  are  :  (1)  the  posterior  longi- 
tudinal bundles  ;  (2)  the  superior  cerebellar  peduncles  or  the  brachia  con- 
junctiva ;  (3)  the  fillet. 

The  posterior  longitudinal  bundle  (Figs.  199  and  200)  is  a  small  compact 


Superior  quadrigeminal  boch* 
Tegmentum  ; 

Inferior  brachium  \ 

Internal  geniculate  bodv  j  \ 

External  geni- 
culate bodysv 


Sylvian  grey  matter 


■   'Sylvian  aqueduct 


Nucleus  of  third 

nerve 
ifr;--  — j-Posterior  longi- 
''/.,   *   tudinal  bundle 
-,    /  \  •>' 

--Red  nucleus 

—  Fibres  of  superior 
cerebellar  peduncle 


-Fascicles  of 
third  nerve 


Optic  tract 


Crusta 

Mesial  fillet 

Substantia  nigra  Corpus  mammillare 

FlG.  200. — Section  through  upper  part  of  Mesencephalon  at  level  of  superior 
(juadrigeminal  body.  The  drawing  is  taken  from  a  Weigert-Pal  specimen. 
The  dark  colour  of  the  substantia  nigra  is  not  evident  owing  to  the 
thinness  of  the  section. 


tract  which  is  placed  upon  the  outer  aspect  of  the  lower  portion  of  the 
central  grey  matter  of  the  aqueduct. 

The  superior  cerebellar  peduncles  are  two  large  strands  which  are  con- 
tinued upwards  from  the  cerebellum  into  the  mesencephalon.  By  pulling 
back  the  margin  of  the  cerebellum  where  it  overlaps  the  lower  quadri- 
geminal bodies,  these  peduncles  will  be  seen  on  the  surface  as  they  converge 
in  an  upward  direction.  Si  retching  across  the  interval  between  them,  and 
bringing  them  into  continuity  with  each  other,  is  a  thin  lamina  called  the 
valve  of  Vieussens.  When  the  superior  cerebellar  peduncles  reach  the  bases 
of  the  inferior  quadrigeminal  bodies,  they  sink  into  the  substance  of  the 
mesencephalon,  and  in  a  transverse  section  through  the  lower  part  of  this 
portion  of  the  brain  they  may  be  seen  as  two  white  strands,  semilunar  in  out- 

VOL.  II — 33 


5  M  THE   BRAIN 

line,  and  placed  one  on  either  side  of  the  grey  matter  of  the  aqueduct,  As 
they  ascend,  they  gradually  assume  a  deeper  (i.e. ,  a  more  ventral)  position 
in  the  tegmental  part  of  the  mesencephalon,  and  finally  they  decussate  with 
each  other  across  the  mesial  plane  and  proceed  upwards. 

The  term  fillet  is  given  to  two  tracts  presenting  very  different  connexions. 
The  mesial  fillet  (Figs.  199  and  200 )  is  a  sensory  tract  passing  upwards  to 
the  optic  thalamus.  The  lateral  fillet  belongs  to  the  auditory  apparatus, 
and  is  a  part  of  a  chain  through  which  the  cochlear  nucleus  establishes 
connexion  with  the  inferior  quadrigeminal  body.  The  lateral  fillet  can  be 
readily  detected  on  the  outer  free  surface  of  the  lower  part  of  the  tegmentum 
in  the  form  of  some  curved  and  usually  conspicuous  fibres  which  extend 
upwards  and  backwards  to  reach  the  inferior  quadrigeminal  body  and  its 
brachium. 

Within  the  upper  part  of  the  tegmentum  there  is  a  collection  of  nuclear 
matter  which  is  termed  the  red  tegmental  m/eleus,  from  its  ruddy  appearance 
when  seen  in  section.  It  is  rod -like  in  form,  and  extends  upwards  into  the 
tegmental  region  below  the  optic  thalamus.  In  transverse  section  it  presents 
a  circular  outline,  and  it  is  closely  associated  with  the  upward  prolongation 
of  the  fibres  of  the  superior  cerebellar  peduncle.  The  superior  cerebellar 
peduncle  is  an  efferent  tract  from  the  lateral  hemisphere  of"  the  cerebellum, 
and  its  fibres  end  in  the  red  nucleus  and  the  pulvinar  of  the  optic  thalamus 
of  the^opposite  side.  The  tegmentum  of  the  crus  cerebri  may  be  considered 
to  consist  of  two  parts  :  viz.,  a  lower  part,  which  is  subjacent  to  the  inferior 
quadrigeminal  bodies,  and  which  is  largely  occupied  by  the  decussation  of 
the  [superior  cerebellar  peduncles  ;  and  an  upper  pa?i,  subjacent  to  the 
superior  quadrigeminal  bodies,  which  is  traversed  by  the  emerging  bundles 
of  the  third  nerve,  and  which  contains  the  nucleus  ruber. 


BASAL  GANGLIA   OF  THE  CEREBRAL 
HEMISPHERES. 

The  basal  ganglia  of  the  cerebral  hemispheres  still  require 
to  be  examined.  These  are  the  caudate  and  lenticular 
nuclei,  which  together  form  the  corpus  striatum  ;  the  claus- 
trum  ;  and  the  amygdaloid  nucleus.  With  these  it  is  necessary 
also  to  study  the  composition  of  the  optic  thalamus  and  the 
external  and  internal  capsules. 

Dissection. — The  right  and  left  portions  of  what  remains  of  the  cerebrum 
should  be  separated  from  each  other  by  a  mesial  incision.  On  the  left 
portion  the  sulci,  and  convolutions  on  the  under  or  tentorial  surface  of  the 
hemisphere,  may  be  examined  if  this  has  not  been  done  already  on  another 
specimen. 

A  -rries  of  sections  should,  in  the  next  place,  be  made  through  both  the 
right  and  left  portions  of  the  cerebrum,  with  the  view  of  displaying  the  basal 
ganglia.  On  t/ie  right  side  remove  a  succession  of  thin  slices  by  carrying  a 
long  knife  in  a  horizontal  direction  through  the  parts  which  form  and  lie  below 
the  floor  of  the  body  of  the  lateral  ventricle.  It  is  not  advisable  to  proceed 
farther  down  than  the  level  of  the  anterior  commissure. 

On  tlie  left  side  of  the  brain  a  series  of  vertical-transverse  or  coronal 
sections  should  be  made  through  the  remaining  portion  of  the  cerebrum. 


BASAL  GANGLIA  515 

Begin  by  cutting  off  the  portion  in  front  of  the  head  of  the  caudate  nucleus, 
and  then  proceed  steadily  backwards  until  the  hinder  part  of  the  optic 
thalamus  is  reached.  One  of  the  sections  should  be  planned  to  pass 
through  the  anterior  commissure-. 

Caudate  Nucleus. — This  nucleus  has  already  been  partly 
examined    in   connexion  with    the  lateral  ventricle,   into  the 

Claustrum 
Pn  tames 


Genu  of  corpus  callosum 

Anterior  horn  of  lateral  ventricle 

Head  of  caudate  nucleus 

Anterior  limb  of  internal  capsule  - 
Ventricle  v. 

Genu  of  internal  capsule 
Globus  pallidus  -- 
Bundle  of  Vicq  d'Azyr  - 
Posterior  limb  of  internal  capsule  " 

Thalamus  - 

Retrolenticular  part  J 

of  internal  capsule    ' 

Tail  of  caudate  nucleus  •  • 

Hippocampus  major 

Splenium  ' 

Posterior  horn  of  lateral  ventricle  - 
Band  of  Vicq  d'Azyr  — 

Calcarine  fissure  - 


Tapetum 


Optic  radiation 


ferior  longitudinal  bundle 


FlG.  201. — Horizontal  section  through  the  Right  Cerebral  Hemisphere  at  the 
level  of  the  widest  part  of  the  lenticular  nucleus. 

cavity  of  which  it  bulges.  It  is  a  pyriform  highly  arched 
mass  of  grey  matter,  which  presents  a  thick  swollen  head  or 
anterior  extremity,  and  a  long  attenuated  tail.  The  head 
projects  into  the  anterior  horn  of  the  lateral  ventricle,  whilst  its 
narrower  part  is  prolonged  outwards  and  backwards  on  the 
floor  of  the  body  of  the  ventricle,  where  it  is  separated  from 
the  optic  thalamus  by  the  taenia  semicircularis.  Finally,  its 
tail  turns  downwards  and  then   forwards  into  the  descending 


5'6 


THE  BRAIN 


horn  of  the  lateral  ventricle,  on  the  roof  of  which  it  is  pro- 
longed until  it  finally  joins  the  amygdaloid  nucleus.  The 
caudate  nucleus,  therefore,  presents  a  free  ventricular  surface 
covered  with  ependyma,  and  a  deep  surface  embedded  in 
the  substance  of  the  cerebrum,  and  for  the  most  part  related 
to  the  internal  capsule. 

Owing  to  its  arched  form,  it  follows  that  in  horizontal 
sections  below  a  particular  level  it  is  cut  at  two  points,  and 
both  the  head  and  the  tail  must  be  looked  for  in  the  field  of 


Great  longitudinal  fissure 

Genu  of  corpus  callosum 


Corpus  callosum  (genu) 

Great  longitudinal  fissure 


Caudate  nucleus 
Caudate  nucleus  (in  section) 
Anterior  horn  of  lateral  ventricle 


Fig.  202. — Coronal  section  through  the  Frontal  Lobes  of  the  Cerebrum.  The 
posterior  surface  of  the  anterior  part  of  the  cerebrum  is  depicted  so  that 
the  reader  is  looking  into  the  anterior  horns  of  the  lateral  ventricles  from 
behind. 

section  (Fig.  201).  In  coronal  sections  behind  the  amygdaloid 
nucleus  it  is  also  divided  at  two  places. 

Lenticular  Nucleus. — This  mass  of  grey  matter  lies  on  the 
outer  side  of  the  caudate  nucleus  and  the  optic  thalamus,  and 
is  for  the  most  part  completely  embedded  within  the  white 
medullary  substance  of  the  cerebral  hemisphere.  It  does  not 
occupy  so  much  ground  as  the  nucleus  caudatus.  Indeed,  it 
presents  a  very  close  correspondence  in  point  of  extent  with 
the  island  of  Reil  on  the  surface. 

When  seen  in  horizontal  section  (Fig.  201)  it  presents  a 
shape  similar  to  that  of  a  biconvex  lens.      Its  inner  surface 


BASAL  GANGLIA 


5'7 


bulges  more  than  the  outer  surface,  and  its  point  of  highest 
convexity  is  placed  opposite  the  taenia  semicircularis  or  the 
interval  between  the  caudate  nucleus  and  the  anterior  end  of 
the  optic  thalamus. 

When  seen  in  coronal  section,  the  appearance  presented 
by  the  lenticular  nucleus  differs  very  much  in  the  different 
planes  of  section.      Figure  203  represents  a  section  through 


Corpus  callosum 


Great  longitudinal  fissure 


Lateral  ventricle 

Choroid  plexus 

Foramen  of  Monro 

1 
Anterior  pillar  of  fornix 


Claustruni 


Fig. 


1  Internal  capsule 

Lenticular  nucleus 
Caudate  nucleus 
Septum  lucidum 

203. — Coronal  section  through  the  Cerebrum  so  as  to  cut  through  the 
anterior  part  (putamen)  of  the  lenticular  nucleus.  The  anterior  cut 
surface  of  the  posterior  part  of  the  cerebrum  is  depicted. 


its  anterior  portion.  Here  it  is  semilunar  or  crescentic  in 
outline.  Further,  it  is  intimately  connected  with  the  head 
of  the  caudate  nucleus  by  bands  of  grey  matter  which  pass 
between  the  two  nuclei  and  break  up  the  fore-part  of  the 
internal  capsule.  It  is  due  to  the  ribbed  or  barred  appear- 
ance which  i^  presented  by  such  a  section  as  this  that  the 
term  corpus  striatum  is  given  to  the  two  nuclei. 

When   the  section   is   made   in   a   plane  farther  back,  the 


5i* 


THE  BRAIN 


divided  lenticular  nucleus  assumes  an  altogether  different 
shape,  and  is  seen  to  be  completely  cut  off  from  the  caudate 
nucleus  by  the  internal  capsule  (Fig.  204).  It  is  now  tri- 
angular or  wedge-shaped.  Its  base  is  turned  towards  the 
external  capsule,  the  claustrum,  and  the  island  of  Reil ;  its 
internal  surface  is  applied  to  the  internal  capsule ;  whilst  its 
inferior  surface  is  directed  downwards  towards  the  base  of  the 


Great  longitudinal  fissure 


Choroid  plexus 
Lateral  ventricle 


Claustrum 


Corpus  callosum 
Fornix 

.Velum  interpositum 


Caudate  nucleus 
Vein  of  corpus  striatum 

...  —  Thalamus 
._£.    -Ventricle  ill. 
---ft-    Choroid  plexus 
-f  -Internal  capsule 

»~  -  Foramen  of  Monro 
-'-._    Anterior  pillar  of 

j<K.   jpm..  fornix 

^^■T  1    Optic  tract 

Anterior  commissure 
Optic  nerve 


Globus  pallidus 

Amygdaloid  nucleus  ;       l  I     j  Olfactory  tract 

Bundle  of  Vicq  d'Azy'r      /       ,'         !  Optic  chiasma 
Locus  perforatus  anticus       .;        Infundibulum 

Anterior  pillar  of  fornix 

FlG.  204. — Coronal  section  through  the  Cerebrum  in  such  a  plane  as  to  cut 
the  three  parts  of  the  lenticular  nucleus  ;  the  posterior  cut  surface  of 
the  anterior  part  of  the  cerebrum  is  deDicted. 


brain.  But,  further,  two  white  laminae  are  now  evident,  the 
external  and  the  internal  medullary  lamince,  which  traverse  its 
substance  and  divide  it  into  three  zones.  The  outer,  basal, 
and  larger  zone  is  termed  the  putamen  (Pig.  204).  It  is 
darker  in  colour  than  the  other  two  zones,  and  is  traversed  by 
fine  radiating  white  streaks.  The  two  inner  zones  are  of  a 
faint  yellowish  tint,  and  they  together  form  what  is  termed 
the  globus  fiallidus  (Figs.  204  and  201).  The  putamen  has  a 
greater  antero-posterior  length  than  the  globus  pallidus.      It 


BASAL  GANGLIA  519 

follows  from  this  that  it  alone  is  connected  with  the  head  of 
the  caudate  nucleus  by  the  intervening  bands  of  grey  matter 
(Fig.  203). 

The  nucleus  lenticularis  comes  to  the  surface  at  the 
anterior  perforated  spot,  and  a  continuity  between  the  grey 
matter  forming  it  and  the  grey  cortex  of  the  brain  is  thus 
established. 

Claustrum. — This  is  a  thin  plate  of  grey  substance  em- 
bedded in  the  white  matter  which  intervenes  between  the 
lenticular  nucleus  and  the  grey  cortex  of  the  island  of  Reil 
(Figs.  201  and  204).  Followed  in  an  upward  direction,  it 
becomes  gradually  thinner  until  it  ultimately  appears,  when 
seen  in  section,  as  an  exceedingly  delicate  grey  streak.  As 
it  is  traced  downwards,  however,  it  thickens  considerably, 
and  at  the  base  of  the  brain  it  comes  to  the  surface  at  the 
anterior  perforated  spot,  and  becomes  continuous  with  the 
grey  matter  of  the  cerebral  cortex.  Its  extent  corresponds  very 
nearly  with  the  area  occupied  by  the  island  of  Reil,  and  its 
surface  towards  this  portion  of  the  cerebral  cortex  shows^ ridges 
and  depressions  corresponding  to  the  insular  gyri  and  sulci. 

Internal  Capsule. — This  term  is  applied  to  the  broad  band 
of  white  matter  which  intervenes  between  the  lenticular 
nucleus  on  the  outside,  and  the  optic  thalamus,  taenia  semi- 
circularis,  and  caudate  nucleus  on  the  inner  side.  In  front 
it  is  much  broken  up  by  the  connecting  bands  of  grey  matter 
which  pass  between  the  head  of  the  caudate  nucleus  and 
the  fore-part  of  the  putamen  of  the  lenticular  nucleus  (Fig. 
203) ;  but  behind  this  it  forms  a  solid  white  mass  of  nerve 
fibres.  When  seen  in  horizontal  section,  the  internal  capsule 
is  observed  to  be  bent  upon  itself  opposite  the  taenia  semi- 
circularis,  or  the  interval  between  the  caudate  nucleus  and 
the  thalamus  (Fig.  201).  This  bend,  which  points  inwards, 
is  called  the  genu.  About  one-third  of  the  internal  capsule 
lies  in  front  of  the  genu,  and  this  part  is  called  the  anterior 
limb ;  the  remaining  two-thirds,  which  lie  behind  the  genu, 
constitute  the  posterior  limb. 

Connexions  of  the  Internal  Capsule.-  -The  internal  capsule 
is  directly  continuous  below  with  the  crusta  of  the  cerebral 
peduncle.  The  dissector  can  easily  satisfy  himself  in  the 
specimens  before  him  of  this  continuity;  it  is  apparent  in  the 
more  posterior  of  the  coronal  sections  which  he  has  made 
through  the  left  portion  of  the  cerebrum. 


52o  THE  BRAIN 

It  has  already  been  mentioned  that  the  fibres  which  occupy  the  middle 
third  or  more  of  the  crusta  of  the  cerebral  peduncle  belong  to  the  motor 
pyramidal  tract.  In  the  internal  capsule  these  occupy  the  anterior  half  of 
the  posterior  limb,  being  thus  placed  immediately  behind  the  genu.  The 
fibres  which  constitute  the  inner  third  of  the  crusta  come  from  the  anterior 
limb  of  the  internal  capsule  ;  whilst  the  fibres  which  form  the  outer  third 
of  the  crusta  are  situated  in  the  posterior  limb. 

When  the  fibres  of  the  internal  capsule  are  traced  upwards,  they  are 
found  to  spread  out  in  a  radiating  or  fan-like  manner  so  as  to  reach  the 
various  convolutions  of  the  cerebral  hemispheres.  This  arrangement  is 
termed  the  corona  radiata.  As  the  fibres  of  the  corona  radiata  are 
liberated  from  the  internal  capsule  and  spread  out  to  reach  their  destina- 
tions, they  are  intersected  by  the  system  of  fibres  which  comes  from  the 
corpus  callosum,  and  which  also  radiate  in  every  direction  to  gain  the 
cortex  of  the  cerebrum. 

Nuclei  of  the  Optic  Thalamus. — When  a  horizontal  section 
is  made  through  the  optic  thalamus  in  a  fresh  brain,  or  in  one 
which  has  been  preserved  by  means  of  formalin  or  a  chromic 
salt,  the  grey  matter  composing  it  is  seen  to  be  broken  up 
into  an  external,  an  internal,  and  an  anterior  nucleus  by  thin 
white  medullary  laminae. 

External  Capsule.  —  This  term  is  applied  to  the  thin 
stratum  of  white  matter  which  intervenes  between  the 
lenticular  nucleus  and  the  claustrum  (Figs.  201  and  204). 

Dissection. — The  bundle  of  Vicq  d'Azyr  and  the  anterior  commissure 
should  now  be  followed  as  far  as  this  is  possible  in  what  remains  of  the 
right  half  of  the  cerebrum.      In  neither  case  is  the  dissection  a  difficult  one. 

By  removing  the  remains  of  the  lenticular  nucleus  the  anterior  commissure 
will  be  exposed  in  its  course  towards  the  temporal  lobe.  In  the  first 
instance,  it  passes  transversely  outwards  through  the  lower  part  of  the 
globus  pallidus  and  below  the  putamen.  It  then  bends  suddenly  backwards 
to  reach  the  medullary  centre  of  the  temporal  lobe,  above  the  descending 
horn  of  the  lateral  ventricle.  If  the  dissection  be  successfully  accomplished, 
the  anterior  commissure  will  be  seen  to  present  a  twisted  or  rope-like 
appearance. 

The  bundle  of  Vicq  d'Azyr  may  be  traced  from  the  corpus  mammillare 
upwards  into  the  anterior  nucleus  of  the  optic  thalamus  by  scraping  away 
the  grey  matter  on  the  side  of  the  third  ventricle.  The  continuity  between 
the  anterior  pillar  of  the  fornix  and  the  corpus  mammillare  should  at  the 
same  time  be  established.  Within  the  corpus  mammillare  there  is  a  nucleus 
of  grey  matter. 


THE  PARTS  OF  THE  BRAIN   WHICH   LIE  IN 
THE  POSTERIOR  CRANIAL  FOSSA. 

The  parts  which  lie  below  the  tentorium  cerebelli  in  the 
posterior  cranial  fossa  are  the  medulla  oblongata,  the  pons 
Varolii,  and  the  cerebellum.     These  are  grouped  around  the 


MEDULLA  OBLONGATA 


52i 


fourth  ventricle  of  the  brain — a  cavity  which  communicates 
below  with  the  central  canal  of  the  spinal  cord,  and  above 
with  the  aqueduct  of  Sylvius.  Through  the  latter  it  establishes 
a  connexion  with  the  third  ventricle  of  the  brain. 

Medulla  Oblongata. — This  is  the  continuation  of  the  spinal 
cord  into  the  brain.  It  is  not  more  than  one  inch  in  length, 
and  may  be  reckoned  as  beginning  at  the  level  of  the  foramen 
magnum.      From   this  it   proceeds  upwards  in  a  very  nearly 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum ^ 

externum    j 
Corpus  geniculatum  _^ 
internum 
Locus  perforatus 
posticus 


Middle  peduncle 
of  cerebellum 


Restiform  body 

Olive 

Pyramid 

Anterior  superficial 

arcuate  fibres 

Decussation  of 
pyramid 


Optic  nerve 
Infundibulum 
Tuber  cinereum 

Corpus  mammillare 
\    Oculo-motor  nerve 
-—(in.) 

'     Trochlear  nerve  (iv.) 
—  winding  round  crus 

cerebri 


Trigeminal  nerve  (v.) 
Abducent  nerve  (vi.) 
Facial  nerve  (vn.) 
Auditory  nerve  (vin.) 

Vago-glosso-phary  n  - 
geal  nerve  (ix.  and  x.) 

Fascicles  of  hypo- 
glossal nerve  (XII.) 
cut  short 

Spinal  accessory 
nerve  (xi.) 

First  cervical  nerve 


FlG.  205. — Front  view  of  the  Medulla,  Pons,  and  Mesencephalon 
of  a  full-time  Fcetus. 


vertical  direction,  and  ends  at  the  lower  border  of  the  pons 
Varolii.  At  first  its  girth  is  similar  to  that  of  the  cord,  but  it 
rapidly  expands  as  it  approaches  the  pons,  and  consequently 
it  presents  a  more  or  less  conical  appearance.  Its  anterior 
surface   lies   behind   the  groove  on  the  basilar  portion  of  the 

ipital  bone,  whilst  its  posterior  aspect  is  sunk  into  the 
vallecula  of  the  cerebellum. 

The  medulla  oblongata  is  a  bilateral  structure,  and  this  is 
evident  even  on  an   inspection  of  its  exterior.      The  antero- 


522 


THE  BRAIN 


median  and  posteromedian  grooves  on  the  surface  of  the 
spinal  cord  are  prolonged  upwards  on  the  anterior  and  posterior 
faces  of  the  medulla. 

The  antero-median  groove,  as  it  passes  from  the  cord  on  to 
the  medulla,  is  interrupted  at  the  level  of  the  foramen  magnum 
by  several  strands  of  fibres  which  cross  the  mesial  plane  from 
one  side  to  the  other.  This  intercrossing  is  termed  the 
decussation  of  the  pyramids.  Above  this  level  the  furrow  is 
carried  upwards  to  the  lower  border  of  the  pons.  Here  it 
expands  slightly,  and  ends  in  a  blind  pit,  termed  the  foramen 
ccecum  of  Vicq  d'Azyr. 

The  poster o-median  fissure  is  only  carried  up  for  half  the 
length  of  the  medulla.  At  this  point  the  central  canal  of  the 
cord  opens  on  the  dorsal  aspect  of  the  medulla,  and  the  lips 
of  the  postero-median  fissure  are  thrust  widely  apart  from  each 
other,  so  as  to  constitute  the  limits  of  a  triangular  area,  which 
forms  on  the  posterior  surface  of  the  medulla,  the  lower  part 
of  the  fossa  rhomboidalis,  or  the  floor  of  the  fourth  ventricle. 
The  dissector  is  now  in  a  position  to  understand  the  terms 
"  closed  "  and  "  open  "  as  applied  to  different  portions  of  the 
medulla.  The  lower  half  of  the  medulla,  containing  as  it 
does  the  central  canal  in  its  interior,  is  the  closed  part)  the 
upper  half  (above  the  opening  of  the  central  canal),  which  by 
its  dorsal  surface  forms  the  lower  part  of  the  floor  of  the  fourth 
ventricle,  is  the  open  part  of  the  medulla. 

The  surface  of  each  lateral  half  of  the  medulla  should  now 
be  studied.  It  is  well,  however,  to  defer  for  a  little  the 
examination  of  the  medullary  part  of  the  floor  of  the  fourth 
ventricle.  The  dissector  has  already  noticed  two  linear  rows 
of  nerve  fascicles  issuing  from  and  entering  the  medulla  on 
each  side.  The  anterior  row  consists  of  the  roots  of  the 
hypoglossal  and  the  uppermost  part  of  the  anterior  root  of  the 
first  cervical  nerve.  They  continue  upwards  on  the  medulla 
in  the  line  of  the  anterior  nerve  roots  of  the  spinal  cord,  and 
they  emerge  along  the  bottom  of  a  more  or  less  distinct  groove. 
The  posterior  row  is  formed  of  the  nerve  fascicles  of  the  spinal 
accessory,  vagus,  and  glossopharyngeal  nerves,  and  they  lie  in 
series  with  the  posterior  roots  of  the  spinal  nerves. 

By  these  two  rows  of  nerve  fascicles,  each  side  of  the 
medulla  is  divided  into  three  districts,  viz.,  an  anterior,  a 
lateral,  and  a  posterior,  similar  to  the  surface  areas  of  the 
three  columns  on  the  side  of  the  cord.      At  first  sight,  indeed, 


ANTERIOR  AREA  OF  THE  MEDULLA       523 

they  appear  to  be  a  direct  continuation  upwards  of  these 
portions  of  the  cord  ;  it  is  easily  demonstrated,  however,  that 
this  is  not  the  case,  and  that  the  fibres  in  the  three  columns 
of  the  cord  undergo  a  rearrangement  as  they  are  traced  into 
the  medulla. 

Anterior  Area  of  the   Medulla — Pyramid. — The   district 


N.H.  Nucleus  hypoglossi. 
N.V.  Vagoglossopharyngeal 

nucleus. 
I  .S.    Fasciculus  solitarius. 
X.A.    Nucleus  ambiguus. 


CROSSED  PYR.TR. 


DIR.PYR.TR. 


Fig.  206. — Diagram  oi  the  Decussation  of  the  Pyramids. 
(Modified  from  Van  Gehuchten.) 

between  the  antero-median  furrow  and  the  row  of  hypoglossal 
nerve  fascicles  issuing  from  the  medulla  receives  the  name  of 
the  pyramid.  An  inspection  of  the  surface  is  almost  sufficient 
to  show  that  this  is  formed  by  a  compact  mass  of  longitudinally 
directed  fibres.  It  expands  somewhat,  and  assumes  a  more 
prominent  appearance  as  it  passes  upwards,  and,  finally  reach- 
ing the  lower  border  of  the  pons  Varolii,  it  becomes  slightly 
constricted  and  disappears   from   view  by  plunging  into  that 


524 


THE  BRAIN 


structure.      The  pyramids  are  the  great  motor  strands  of  the 
medulla. 

Although  the  pyramid  at  first  sight  appears  to  be  the  con- 
tinuation upwards  of  the  anterior  column  of  the  cord,  it 
contains  within  itself  only  a  very  small  proportion  of  fibres 
which,  lower  down,  occupy  that  column  of  the  cord.  This 
will  be  at  once  manifest  if  the   decussation   of  the  pyramids 

Optic  tract 

Crus  cerebri 

^'Corpus  geniculatum  externum 

Pulvinar 

Corpus  geniculatum  internum 

Superior  brachium 
Inferior  brachium 
Inferior  quadrigeminal  body 
Lateral  fillet 


Superior  cerebellar  peduncle 
Taenia  pontis 

Middle  peduncle  of  the  cerebellum 


Restiform  body 

Ligula 

Olive 
— .Arcuate  fibres 
~~"Clava 
"~~Cuneate  tubercle 

Roland  ic  tubercle 

Lateral  district  of  medulla 

Anterior  column  of  cord 


Fig.  207. — Lateral  view  of  the  Medulla,  Pons,  and  Mesencephalon 
of  a  full-time  Foetus. 


be  examined.  For  this  purpose  introduce  the  back  of  the 
knife-blade  into  the  antero- median  furrow  below  the  de- 
cussation, and  on  one  side  push  forcibly  outwards  the 
anterior  column  of  the  cord.  The  pyramid  will  then  be 
seen  to  divide  at  this  level  into  two  portions,  viz.,  a  small 
strand  termed  the  direct  pyramidal  tract,  which  proceeds 
downwards  into  the  anterior  column  of  the  cord,  and  takes  up 
a  position  close  to  the  antero-median  furrow,  and  a  much 
larger  strand  called  the  crossed  pyramidal  tract,  which  at  this 
level  is  broken   up  into  three  or  more  coarse  bundles  which 


LATERAL  AREA  OF  THE   MEDULLA         525 

sink  backwards,  and,  at  the  same  time,  cross  the  mesial  plane 
to  take  up  a  position  in  the  opposite  lateral  column  of  the 
cord,  close  to  the  posterior  horn  of  grey  matter.  It  is  the 
intercrossing  of  the  corresponding  bundles  of  the  crossed 
pyramidal  tracts  of  opposite  sides  which  produces  this  char- 
acteristic decussation. 

But  if  the  direct  pyramidal  tract  in  the  anterior  column  of  the  cord 
is  alone  represented  in  the  corresponding  district  of  the  medulla,  it 
may  be  asked  :  What  becomes  of  the  larger  lateral  part  of  the  anterior 
column  of  the  spinal  cord  in  the  medulla?  It  is  thrust  aside  by  the 
decussating  bundles  of  the  crossed  pyramidal  tract,  and  thus  comes  to 
occupy  a  deep  position  in  the  medulla. 

Lateral  Area  of  the  Medulla. — This  is  the  district  on  the 
surface  of  the  medulla  which  is  included  between  the  two 
rows  of  nerve  roots,  viz.,  the  hypoglossal  roots  in  front,  and 
the  root  fascicles  of  the  spinal  accessory,  vagus,  and  glosso- 
pharyngeal behind.  It  presents  a  very  different  appearance 
in  its  upper  and  lower  parts.  In  its  lower  portion  it  appears 
to  the  eye  as  a  continuation  upwards  of  the  lateral  area  of 
the  cord:  in  its  upper  part  is  seen  the  striking  oval  prominence, 
which  receives  the  name  of  the  olivary  eminence. 

The  lower  part  of  this  district,  however,  is  very  far  from 
being  an  exact  counterpart  of  the  lateral  column  of  the  cord. 
As  we  have  already  observed,  the  large  crossed  pyramidal 
tract,  which  in  the  cord  lies  in  the  lateral  column,  is  not 
present  in  this  district  of  the  medulla ;  above  the  decussation 
of  the  pyramids  it  forms  the  chief  part  of  the  pyramidal  tract 
of  the  opposite  side.  Another  small  strand  of  fibres,  the 
direct  cerebellar  tract,  prolonged  upwards  in  the  lateral  column 
of  the  cord,  gradually  leaves  this  portion  of  the  medulla. 
This  tract  of  fibres  lies  on  the  surface,  and  it  is  often  visible 
to  the  naked  eye  as  a  white  streak  inclining  obliquely  back- 
wards into  the  posterior  district  of  the  medulla  to  join  its 
upper  part,  i.e.,  the  restiform  body.  The  great  majority  of 
the  remainder  of  the  fibres  which  are  prolonged  upwards  from 
the  lateral  column  of  the  cord  disappear  from  the  surface  at 
the  lower  border  of  the  olivary  eminence,  by  dipping  into  the 
substance  of  the  medulla  under  cover  of  that  projection.  A 
narrow  band,  however,  may  be  noticed  to  be  carried  upwards 
to  the  pons  in  the  interval  which  exists  between  the  posterior 
border  of  the  olive  and  the  roots  of  the  vagus  and  glosso- 
pharyngeal nerves. 


526 


THE   BRAIN 


The  olivary  eminence  is  a  smooth  oval  projection,  which 
occupies  the  upper  part  of  the  lateral  area  of  the  medulla. 
Its  long  axis,  which  is  vertical,  is  about  half  an  inch  long, 
and  its  upper  end  is  separated  from  the  lower  border  of  the 
pons  Varolii  by  an  interval  or  groove. 

Posterior  Area  of  the  Medulla.  —  In  its  lower  half  this 
district  is  bounded  behind  by  the  postero-median  fissure,  and 
in  its  upper  half  by  the  lateral  margin  of  the  medullary 
portion  of  the  floor  of  the  fourth  ventricle.      In  front  it  is 

Pineal  body 

Superior 
quadrigeminal  body 


Frenulum 


Valve  of  Vieussens 


Superior  peduncle  of 
the  cerebellum 

Middle  peduncle  of. 
the  cerebellum 


Striae  acusticae 

Area  acustica 

Trigonum  vagi 

Cuneate  tubercle 
Funiculus  gracilis 


Inferior 
quadrigeminal  body 


Crus  cerebri 

Pontine  part  of  floor 
of  ventricle  iv. 

Eminentia  teres 
Fovea  superior 

Restiform  body 
Trigonum  hypoglossi 

Clava 

Roland ic  tubercle 

Funiculus  cuneatus 


FiG.  208. — Back  view  of  the  Medulla,  Pons,  and  Mesencephalon 
of  a  full-time  Foetus. 

separated  from  the  lateral  area  by  the  row  of  root-fascicles 
belonging  to  the  spinal  accessory,  vagus,  and  glossopharyngeal 
nerves.  As  in  the  lateral  area,  we  recognise  a  lower  portion 
and   an   upper  portion,  which   are   quite  distinct  from   each 

other. 

The  lower  part  of  the  posterior  area  corresponds  more  or 
less  closely  with  the  posterior  columns  of  the  cord.  It  will 
be  remembered  that  in  the  cervical  part  of  the  cord  the 
posterior  columns  are  divided  by  a  distinct  septum  of  pia 
mater  into  an  inner  postero-median  strand  (column  of  Goll) 
and  an  outer  postero- external  strand  (column  of  Burdach). 


POSTERIOR  AREA  OF  THE   MEDULLA      527 

These  are  prolonged  upwards  into  the  medulla,  and  in  the 
lower  part  of  the  posterior  area  they  stand  out  distinctly,  and 
are  separated  from  each  other  by  a  continuation  upwards 
from  the  cord  of  the  paramedian  groove.  In  the  medulla 
these  strands  receive  different  names.  The  inner  one  is  called 
the  funiculus  gracilis,  whilst  the  outer  one  is  designated  the 
funiculus  cuneatus.  Each  of  these  strands,  when  it  reaches 
the  lower  part  of  the  floor  of  the  fourth  ventricle,  ends  in  a 
slightly  expanded  prominence.  The  swollen  extremity  of  the 
funiculus  gracilis  is  called  the  clava ;  it  is  thrust  aside  from 
its  neighbour  of  the  opposite  side  by  the  opening  up  of  the 
medulla  to  form  the  floor  of  the  fourth  ventricle,  and  the 
central  canal  of  the  cord  opens  on  the  surface  in  the  angle 
between  the  two  clavae.  The  thickened  end  of  the  cuneate 
funiculus  receives  the  name  of  the  cuneate  tubercle,  but  it  is 
only  in  the  young  brain  that  it  is  well  marked. 

In  sections  through  this  region  of  the  medulla,  it  is  seen 
that  the  prominences  produced  by  these  two  strands  and  their 
enlarged  extremities  are  in  a  great  measure  due  to  the  presence 
of  two  elongated  nuclei  or  collections  of  grey  matter  which 
lie  subjacent  to  them,  and  which  gradually  increase  as  they 
are  traced  upwards.  These  are  termed  respectively  the 
gracile  and  the  cuneate  nuclei,  and  it  can  be  easily  shown  that 
as  the  grey  matter  increases  in  quantity  the  fibres  of  the  two 
corresponding  strands  diminish  in  number.  Indeed,  it  is 
doubtful  if  any  of  their  fibres  are  prolonged  upwards  beyond 
the  level  of  the  nuclei. 

But  a  third  longitudinal  elevation  is  also  apparent  in  the 
lower  part  of  the  posterior  area  of  the  medulla.  This  is 
placed  on  the  outer  side  of  the  funiculus  cuneatus — between 
it  and  the  posterior  row  of  nerve  roots — and  it  has  no  counter- 
part in  the  posterior  column  of  the  cord.  It  is  called  the 
funiculus  of  Rolando,  because  it  is  produced  by  the  substantia 
gelatinosa  Rolandi  approaching  the  surface  along  this  line. 
Extremely  narrow  below,  the  funiculus  of  Rolando  widens 
somewhat  as  it  is  traced  upwards,  and  finally  ends  in  an 
expanded  extremity  called  the  tubercle  of  Rolando.  The  thin 
layer  of  fibres  which  appear  on  the  surface  of  the  tubercle 
and  funiculus  of  Rolando  and  cover  the  substantia  Rolandi  in 
this  position  belong  to  the  spinal  root  of  the  trigeminal  nerve. 

The  restiform  body  forms  the  upper  part  of  the  posterior 
area.      It  lies  between  the  lower  part  of  the  floor  of  the  fourth 


528  THE  BRAIN 

ventricle  and  the  roots  of  the  vagus  and  glossopharyngeal 
nerves,  and  is  thrust  outwards  by  the  opening  up  of  the 
medulla.  It  is  a  large  rope-like  strand,  which  inclines  upwards 
and  outwards,  and  then  finally  takes  a  turn  backwards,  and 
enters  the  cerebellum,  of  which  it  constitutes  the  inferior 
peduncle.  The  restiform  body,  therefore,  is  to  be  regarded  as 
the  main  connexion  between  the  cerebellum  above  and  the 
medulla  and  spinal  cord  below.  At  the  same  time,  it  must 
be  understood  that  it  is  not  formed  of  fibres  which  are  pro- 
longed into  it  from  the  funiculus  gracilis  and  funiculus  cuneatus 
of  its  own  side.  It  is  true  that  a  surface  inspection  of  the 
medulla  might  very  naturally  lead  to  this  supposition,  because 
there  is  no  sharp  line  of  demarcation  marking  it  off  from  the 
tubercles  of  these  strands. 

The  fibres  which  build  up  the  restiform  bodies  come  from  several  differ- 
ent sources.  It  will  be  sufficient  to  indicate  the  more  important  of  these — 
(i)  from  the  lateral  column  of  the  spinal  cord  through  the  direct  cerebellar 
tract ;  (2)  from  the  cerebellum  as  the  cerebello-olivary  fibres  which  go  to 
the  opposite  inferior  olivary  nucleus  ;  (3)  from  the  cuneate  and  gracile 
nuclei  of  both  sides  in  the  form  of  the  arcuate  fibres. 

Superficial  Arcuate  Fibres. — On  the  surface  of  the  medulla, 
more  particularly  in  the  neighbourhood  of  the  lower  border 
of  the  olive,  a  number  of  curved  bundles  of  fibres,  termed 
the  anterior  superficial  arcuate  fibres,  may  be  noticed.  They 
vary  greatly  in  number  and  in  distinctness,  and  they  are 
sometimes  so  numerous  as  to  cover  over  almost  entirely  the 
olivary  eminence.  An  attentive  examination  will  show  that 
they  come  to  the  surface  in  the  antero-median  groove  between 
the  pyramids,  frequently  in  the  groove  between  the  pyramid 
and  the  olive,  and  sometimes  also  through  the  substance  of 
the  pyramids.  But  at  whatever  point  they  reach  the  surface, 
the  majority  have  one  destination,  viz.,  the  restiform  body — a 
considerable  part  of  which  they  form.  They  are  derived  from 
the  cuneate  and  gracile  nuclei  of  the  opposite  side. 

The  posterior  superficial  arcuate  fibres  arise  in  the  cuneate 
and  gracile  nuclei,  and  enter  the  restiform  body  of  the  same 
side. 

Dissection. — The  pyramid  of  one  side  should  now  be  carefully  raised. 
When  dislodged  from  its  bed  it  should  be  gently  pulled  upwards  towards 
the  pons  Varolii.  In  this  way  its  entrance  into  the  pons  is  brought 
very  clearly  into  view,  and  further,  numerous  arcuate  fibres  will  be  seen 
running  forwards  upon  the  mesial  aspect  of  the  opposite  pyramid  to  reach 
the  surface. 


STRUCTURE  OF  THE  MEDULLA 


529 


Very  little  of  the  structure  of  the  medulla  can  be  learnt  from  specimens 
obtained  in  the  dissecting-room.  Further,  it  is  not  advisable  to  cut  into 
the  medulla  at  present,  because  the  student  has  still  to  study  that  portion 
of  its  dorsal  surface  which  forms  the  lower  part  of  the  floor  of  the  fourth 
ventricle,  and  this  cannot  advantageously  be  done  until  the  cerebellum  has 
been  examined.  Still,  it  is  convenient  to  say  what  little  has  to  be  said  on 
the  structure  of  the  medulla  at  this  stage. 

Structure  of  the  Medulla.  — When  transverse  sections  are  made  through 
the  medulla  at  different  levels,  a  faint  line  called  the  median  raphe,  and 
occupying  the  mesial  plane,  is  seen  to  divide  it  into  two  exactly  similar 
lateral  portions.  The  raphe  is  formed  by  the  close  intersection  of  fibres 
running  in  different  directions. 

Each  half  of  the  medulla  is  composed  of  {a)  strands  of  white  matter  ; 
{b)  grey  matter,  which  is  present  both  in  the  form  of  direct  continuations 
into  the  medulla  of  portions  of  the  grey  matter  of  the  cord,  and  also  in  the 


( iracile  nucleus 


Cuneate  nucle 


Cuneate  nucleus 

Spinal  root  of  fifth  nerve 

Substantia  gelatinosa 

Rolandi 

Direct  cerebellar  tract 

Crossed  pyramidal  trad 


Detached  anterior 
horn  of  grey  matter 

Decussation  of  pyramids 


Anterior  basis-bundle 
Fig.  209. — Section  through  the  lower  part  of  the  Medulla  of  the  Orang. 


form  of  isolated  clumps,  which  are  not  represented  in  the  cord  ;  and  {c)  the 
formatio  reticularis,  a  substance  which  is  composed  of  grey  matter  coarsely 
broken  up  by  fibres  which  traverse  it  in  different  directions.  The  white- 
matter,  as  in  the  cord,  is  for  the  most  part  disposed  on  the  surface  and  the 
grey  matter  in  the  interior,  but  in  the  open  part  of  the  medulla  the  grey 
matter  comes  to  the  surface  on  its  dorsal  aspect,  and  is  spread  out  over 
that  area  which  forms  the  medullary  portion  of  the  floor  of  the  fourth 
ventricle. 

When  the  grey  matter  of  the  cord  is  traced  up  into  the  medulla,  many 
striking  changes  in  its  arrangement  become  apparent.  Owing  to  the 
increase  in  size  of  the  large  wedge-shaped  graoile  and  cuneate  funiculi,  the 
posterior  horns  of  grey  matter  become  folded  outwards,  so  that  they  soon 
assume  a  position  at  right  angle,  to  the  mesial  plane,  and  lie  very  nearly 
in  the  same  transverse  line.  At  the  same  time,  the  cuneate  and  gra< ale 
nuclear  columns  of  grey  matter  which  grow  out  from  the  basal  portion  of 

this  horn  and  underlie  the  strands  of  the   same  name,  begin   to   make  their 

appearance.     From  the  deep  aspect  of  these  nuclei,  fibres,  which   I 

origin  within  them,  stream  forwards  and  inwards  through  the  cervical  pot 
tion  of  the  posterior  horn,  so  as  to  reach  the  raphe.     The  caput  cornu  is  in 
VOL.   II — 34 


53o  THE  BRAIN 

this   way  cut  oft"  from   the    basal   portion.     The   latter  remains  in  close 


Funiculus  gracilis 

Funiculus 
cuneatus 


Spinal  root 
of  fifth  nerve 


Formatio 
reticularis 


Gracile  nucleus 


Cuneate 

nucleus 


Direct 

cerebellar — \^{*s«^ 
tract 


Lower  end 
of  olivary 
eminence 


Substantia 
gelatinosa 
Rolandi 

Decussation 
of  the  fillet 


Internal 
—accessory 
olivary  nucleus 
Fascicles  of  the 
hypoglossal 
nerve 


Pyramid 


Fig.  210. — Transverse  section  through  the  closed  part  of  the  Medulla  of  a 
full-time  Fcetus  above  the  Decussation  of  the  Pyramid,  treated  by  the 
Weigert-Pal  method.  The  grey  matter  is  white,  and  the  medullated 
strands  of  nerve  fibres  are  rendered  black. 


relation  to  the  central  canal,   whilst  the  caput   or   substantia   gelatinosa 


Gracile  nu 


Grey  matter 
round  canal 


Funiculus 
gracilis 


Funiculus 

cuneatus 

Spinal  root  of 
fifth  nerve  . 

Substantia 
gelatinosa 
Rolandi 


Central  canal 


Decussation 
of  pyramids 


Detached  head  of 
anterior  cornu  of 
grey  matter 


Ipfc ':r'\S    Lateral  part  of  anterior 
column  pushed  aside 
by  decussation 


Antero-median  furrow 

Fig.  211. — Transverse  section  through  lower  end  of  the  Medulla  of  a  full- 
time  Foetus,  treated  by  the  Weigert-Pal  method.  The  grey  matter  is 
therefore  bleached  white  ;   whilst  the  medullated  tracts  are  black. 


Rolandi  is  placed  close  to  the  surface,  enlarges  as  it  is  traced  upwards,  and 
forms  the  prominence  on  the  surface  which  has  already  been  described  as 


STRUCTURE  OF  THE  MEDULLA 


D>3 


the  funiculus  and  tubercle  of  Rolando.  The  fibres  which  have  thus  broken 
up  the  cervical  part  of  the  posterior  horn,  and  which  come  from  the  cuneate 
and  gracile  nuclei,  are  termed  the  internal  or  deep  arcuate  fibres.  They 
reach  the  raphe  on  the  deep  or  dorsal  aspect  of  the  pyramids,  and,  crossing 
the  mesial  plane,  they  form  a  very  complete  decussation  with  the  corre- 
sponding fibres  of  the  opposite  side,  which  is  termed  the  decussation  of  the 
fillet  or  the  sensory  decussation,  in  contradistinction  to  the  term  motor  decus- 
sation, which  is  sometimes  applied  to  the  crossing  of  the  pyramids.  As 
soon  as  they  reach  the  opposite  side  of  the  medulla,  these  internal  or  deep 
arcuate  fibres  turn  upwards  and  form  a  longitudinal  tract,  placed  close  to 
the  raphe  and  on  the  dorsal  aspect  of  the  corresponding  pyramid,  which 
receives  the  name  of  the  fillet  or  lemniscus. 

The  anterior  horn  of  grey  matter  shares  a  like  fate  in  the  medulla,  but 


Gracile 
nucleus 

Cuneate 
nucleus 

Substantia 

gelatinosa 

Rolandi 


Funiculus 
gracilis 

Funiculus 
cuneatus 


Spinal  root  of 
the  trigeminal 
nerve 


Internal 

accessory 

olivary 

nucleus 

Hypoglossal 

nerve 


Pyramid 


FlG.  212. — Transverse  section  through  the  Medulla  of  new-born  Child  at  the 
level  of  the  lower  part  of  the  olivary  eminence,  stained  by  the  Weigert-Pal 
method. 


at  a  lower  level,  at  the  hands  of  the  crossed  pyramidal  tract.  This  great 
bundle,  in  passing  from  the  pyramid  into  the  lateral  column  of  the  cord  of 
the  opposite  side,  traverses  the  anterior  horn  so  as  to  completely  break  up 
its  intermediate  part  and  separate  its  head  from  its  basal  portion.  The 
further  history  of  the  detached  head  we  need  not  trace,  but  it  is  well  to 
observe  that  the  basal  part  of  the  anterior  horn  of  grey  matter  remains  in 
position  on  the  ventral  and  lateral  aspect  of  the  central  canal. 

As  we  proceed  up  the  closed  part  of  the  medulla,  the  central  canal, 
surrounded  by  the  basal  portions  of  the  two  horns  of  grey  matter,  gradually 
inclines  towards  the  dorsal  aspect,  until  it  finally  opens  on  the  surface. 
The  grey  matter  which  surrounds  it  is  now  spread  out  on  the  floor  of  the 
fourth  ventricle,  and  in  such  a  manner  that  the  portion  which  corresponds 
to  the  basal  part  of  the  anterior  horn  of  the  cord  is  situated  close  to  the 
mesial  plane,  whilst  the  part  which  represents  the  base  of  the  posterior 
horn  occupies  a  more  lateral  position.  This  is  important,  because  the 
nucleus  of  origin  of  the  h;  I  nerve  is  placed  in  the  mesial  part  of 


S32 


THE  BRAIN 


the  floor,  whilst  the  nucleus  of  termination  of  the  vagus  and  glossopharyn- 
geal nerves  lies  in  the  lateral  part  of  the  floor. 

The  most  conspicuous  of  the  isolated  clumps  of  grey  matter  in  the 
medulla  are  the  olivary  nucleus  and  the  two  accessory  olivary  nuclei.  The 
olivary  nucleus  lies  subjacent  to  the  olivary  eminence,  and  is  a  very  con- 
spicuous object  in  transverse  sections  through  this  region.  In  such  cases 
it  presents  the  appearance  of  a  thick  wavy  or  undulating  line  of  grey  matter 
folded  upon  itself  so  as  to  enclose  a  space  filled  with  white  matter  and  open 
towards  the  mesial  plane.  It  is  in  reality  a  lamina  arranged  in  a  purse- 
like manner  with  its  open  mouth  directed  towards  the  raphe.  The  fibres 
which  enter  through  its  mouth  constitute  the  olivary  peduncle. 

The  accessory  olivary  nuclei  are  two  band-like  laminae  of  grey  matter. 


Floor  of 
ventricle  IV 

Restiform 
body 

Vagus  nerve 

Posterior 
longitudinal     \  i^VrV 
bundle       v  \ 


Fillet 

Mesial 

accessory 

olivary 

nucleus 


Hypoglossal  \"£;^^^^^K 


Ligula 


Fasciculus 
solitarius 


Dorsal 
accessory 
olivary 
nucleus 


Olivary 
nucleus 


Pyramid 


Fit;.  213. — Transverse  section  through  the  Medulla  at  the  level 
of  the  mid-point  of  the  olive  ("Weigert-Pal  stain). 

which  are  respectively  placed  on  the  dorsal  and  mesial  aspects  of  the  main 
nucleus.  When  seen  in  transverse  section  each  of  these  nuclei  presents  a 
rod-like  appearance  (Fig.  213). 

Behind,  or  deeper  than,  the  olive  and  pyramid  is  the  formatio  reticularis 
of  the  medulla.  It  forms  a  large  part  of  its  substance,  and  is  divided 
into  a  lateral  and  a  mesial  field  by  the  nerve  fascicles  of  the  hypoglossal 
as  they  traverse  the  substance  of  the  medulla  to  reach  the  surface.  In  the 
lateral  portion,  which  lies  behind  the  olive,  there  is  a  considerable  quantity 
of  grey  matter,  continuous  with  that  of  the  cord,  present  in  the  reticular 
formation  ;  it  is  therefore  called  the  formatio  grisea.  In  the  mesial  part, 
however,  which  lies  behind  the  pyramid,  the  grey  matter  is  extremelv  scantv. 
and  the  reticular  matter  here  is  termed  the  formatio  alba. 

The  nerve  fibres  which  traverse  the  formatio  reticularis  run  both  in  the 
transverse  and  in  the  longitudinal  direction.     The  transverse  fibres  are  the 


CEREBELLUM  533 

deep  or  internal  arcuate  fibres.  The  longitudinal  fibres  are  derived  from 
different  sources  in  the  two  fields.  In  the  lateral  part  of  the  formation 
they  represent  the  fibres  of  the  lateral  column  (after  the  removal  of  the 
direct  cerebellar  and  the  crossed  pyramidal  tracts)  which  are  continued  up 
under  cover  of  the  olive.  In  the  mesial  part,  or  formatio  alba,  two 
longitudinal  strands  take  origin,  viz.,  the  fillet  and  the  posterior  longitudinal 
bundle.  Both  lie  close  to  the  raphe.  The  fillet  is  placed  immediately 
behind  the  pyramid,  and  is  formed,  as  described,  by  the  decussating 
internal  arcuate  fibres.  The  posterior  longitudinal  bundle  takes  form  in 
the  upper  part  of  the  medulla,  immediately  subjacent  to  the  grey  matter  of 
the  floor  of  the  fourth  ventricle.  It  is  formed  by  longitudinal  fibres  of  the 
formatio  alba  which  come  from  the  ground-bundle  of  the  anterior  column 
of  the  cord. 

Pons  Varolii. — The  pons  Varolii  is  the  marked  prominence 
on  the  base  of  the  brain  which  is  interposed  between  the 
medulla  and  the  crura  cerebri,  and  which  lies  in  front  of  the 
cerebellum.  It  is  convex  from  side  to  side,  as  well  as  from 
before  backwards,  and  the  transverse  streaks  on  its  surface 
showr  that  superficially  it  is  composed  of  transverse  bundles  of 
nerve  fibres.  On  either  side  these  transverse  fibres  collect 
themselves  together  so  as  to  form  a  large  compact  strand 
which  sinks  in  a  backward  and  outward  direction  into  the 
white  matter  of  the  corresponding  hemisphere  of  the  cere- 
bellum.     This  strand  is  termed  the  middle  cerebellar  peduncle. 

The  ventral  surface  of  the  pons  is  in  relation  to  the  basilar 
process  of  the  occipital  bone  and  the  dorsum  sella?  of  the 
sphenoid  bone.  It  presents  a  mesial  groove  which  gradually 
widens  as  it  is  traced  upwards  (Fig.  205).  In  this  lies 
the  basilar  artery,  but  the  groove  is  not  caused  by  this  vessel ; 
it  is  due  to  the  prominence  which  is  produced  on  either 
side  by  the  passage  downwards  through  the  pons  of  the 
bundles  of  fibres  which  form  the  pyramids  of  the  medulla. 
Where  the  pons  Varolii  becomes  the  cerebellar  peduncle 
the  large  trigeminal  nerve  will  be  seen  emerging  from  its 
ventral  surface,  nearer  its  upper  than  its  lower  border. 

With  the  exception  of  the  restiform  bodies,  the  whole  of 
the  medulla  enters  the  lower  aspect  of  the  pons,  and  its  con- 
stituent parts  are  carried  upwards  within  it.  The  crura 
cerebri  emerge  from  its  upper  aspect.  The  dorsal  surface  of 
the  pons  cannot  be  studied  at  present.  It  is  turned  towards 
the  cerebellum,  which  hides  it  from  view.  It  forms  the  upper 
part  of  the  floor  of  the  fourth  ventricle. 

Cerebellum. — The  cerebellum  is  distinguished  by  the 
numerous  parallel  and  more  or  less  curved  sulci  which 
traverse  its  surface  and  give  it  a  foliated  appearance.      As  in 


534  THE   BRAIN 

the  case  of  the  cerebral  hemispheres,  the  grey  matter  is 
spread  over  the  entire  surface,  whilst  the  white  matter  forms 
in  the  interior  a  central  core. 

In  the  cerebellum  we  recognise  a  median  portion,  termed 
the  vermis,  and  two  lateral  and  much  larger  portions,  called 
the  lateral  hemispheres.  The  distinction  between  these  main 
subdivisions  of  the  organ  is  not  very  evident  from  every  point 
of  view.  In  front,  and  also  behind,  there  is  a  marked 
deficiency  or  notch  (Fig.  214).  The  posterior  notch  is  smaller 
and  narrower  than  the  anterior  notch.  It  is  bounded 
laterally  by  the  hinder  parts  of  the  cerebellar  hemispheres, 
whilst  its  bottom  is  formed  by  the  median  lobe  or  vermis. 
It  is  occupied  by  the  falx  cerebelli.  The  anterior  notch, 
sometimes  termed  the  incisura  semilunaris,  is  much  wider 
than  the  posterior  notch.  When  viewed  from  above,  it  is 
seen  to  be  occupied  by  the  inferior  pair  of  quadrigeminal 
bodies  and  the  superior  cerebellar  peduncles.  As  in  the 
case  of  the  posterior  notch,  the  sides  are  formed  by  the 
lateral  hemispheres,  and  the  bottom  by  the  vermis. 

On  the  superior  surface  of  the  cerebellum,  there  is  little 
distinction  to  be  noted  between  the  median  lobe  and  the 
upper  surface  of  each  lateral  hemisphere.  The  median  lobe 
or  superior  vermis  forms  a  median  elevation,  from  which  the 
surface  slopes  gradually  downwards  on  each  side  to  the 
margin  of  the  hemisphere.  The  vermiform  elevation  is 
highest  in  front,  immediately  behind  the  semilunar  notch, 
and  from  this  it  gradually  inclines  downwards  towards  the 
posterior  notch.  It  receives  the  name  of  the  monticulus 
cerebelli.  The  folia  on  the  surface  of  the  vermis  superior  will 
be  seen  to  be  thicker  and  fewer  in  number  than  those  on 
the  upper  surface  of  the  lateral  hemisphere.  It  is  this 
that  gives  it  the  worm-like  appearance  from  which  its  name 
is  derived. 

On  the  inferior  surface  of  the  cerebellum,  the  distinction 
between  the  three  constituent  parts  of  the  organ  is  much 
better  marked.  On  this  aspect  the  lateral  hemispheres, 
which  are  full,  prominent,  and  convex,  are  separated  by  a 
deep,  mesial  hollow,  which  is  continued  forwards  from  the 
posterior  notch.  This  hollow  is  termed  the  vallecula  cerebelli, 
and  in  its  fore-part  is  lodged  the  medulla  oblongata.  When 
the  medulla  is  raised,  and  the  lateral  hemispheres  pulled 
apart  so  as  to  expose  the  bottom  of  the  vallecula,  it  will  be 


UPPER  SURFACE  OF  CEREBELLUM    535 

seen  that  this  is  formed  by  the  vermis  inferior,  and,  further, 
that  the  latter  is  separated  on  each  side  from  the  correspond- 
ing lateral  hemisphere  by  a  distinct  furrow,  termed  the  sulcus 
vallecula:. 

When  the  margin  of  the  cerebellum,  where  it  forms  the 
bottom  of  the  semilunar  notch  on  the  superior  aspect  of  the 
organ,  is  gently  pushed  backwards,  and  the  mesencephalon 
pulled  forwards,  two  strands  lying  upon  the  dorsal  aspect 
of  the  pons  Varolii  will  be  seen.  These  are  the  superior  cere- 
bellar peduncles.  Emerging  from  the  white  matter  of  the  cere- 
bellum, they  converge  as  they  proceed  upwards,  and  finally 
they  disappear  under  the  inferior  quadrigeminal  bodies.  The 
thin  lamina  which  is  stretched  across  between  them  is  the 
valve  of  Vieussens,  or  the  superior  medullary  velum.  It  is  con- 
tinuous below  with  the  white  core  of  the  cerebellum,  and  it 
forms  the  roof  of  the  upper  part  of  the  fourth  ventricle.  From 
its  dorsal  surface,  close  to  the  inferior  quadrigeminal  body,  the 
small  trochlear  or  fourth  cranial  nerves  emerge. 

Certain  of  the  fissures  which  traverse  the  surface  of  the 
cerebellum,  deeper  and  longer  than  the  others,  map  out 
districts  which  are  termed  lobes.  The  most  conspicuous  of 
all  these  clefts  is  the  great  horizontal  fissure. 

Great  Horizontal  Fissure  of  the  Cerebellum. — The  great 
horizontal  fissure  begins  in  front,  and  passes  round  the  circum- 
ference of  the  cerebellum,  cutting  deeply  into  its  outer  and 
posterior  margins.  In  front,  its  lips  diverge  from  each  other 
so  as  to  enclose  the  large  middle  peduncle,  where  it  passes 
into  the  interior  of  the  cerebellum.  The  great  horizontal 
fissure  divides  the  organ  into  an  upper  and  a  lower  part, 
which  may  be  studied  separately. 

Lobes  on  the  Upper  Surface  of  the  Cerebellum. — When 
examined  from  before  backwards,  the  vermis  superior  presents 
the  following  subdivisions: — (1)  the  lingula \  (2)  the  central 
lobule ;  (3)  the  culmen  monticuli ;  (4)  the  clivus  monticuli  ; 
(5)  the  folium  cacuminis.  With  the  exception  of  the  lingula, 
each  of  these  is  continuous  on  either  side  with  a  correspond- 
ing district  on  the  upper  surface  of  the  hemisphere,  thereby 
forming  a  cerebellar  lobe.  Thus,  the  eentral  lobule  is  pro- 
longed outwards  on  each  side  in  an  expansion  called  the  ala  ; 
the  culmen  constitutes  a  median  connecting  piece  between 
the  two  anterior  crescentic  lobules  of  the  hemispheres ;  the 
clivus   stands   in    the   same   relation    to  the  posterior  crescentic 


536 


THE  BRAIN 


lobules ;  and   the    folium  cacuminis   is    the    connecting    band 
between  the  postero-superior  lobules  of  the  hemispheres. 

.  Lingula. — The  lingula  can  only  be  seen  when  the  bottom 
of  the  semilunar  notch  is  pushed  backwards.  It  consists  of 
four  or  five  small  folia  continuous  with  the  grey  matter  of  the 
vermis  superior,  and  prolonged  forwards  on  the  surface  of  the 
valve  of  Vieussens  or  superior  medullary  velum  in  the  interval 
between  the  superior  cerebellar  peduncles. 

Lobus  Centralis  with  its  Alse. — The  central  lobule  lies  at 

Pons  Varolii 

Mesencephalon 

Central  lobule 


Culmen  monticuli 


Anterior  crescentic  lobule 

Posterior  crescentic  lobule 


Postero-superior 
lobule 


Clivus  monticuli 

Folium  cacuminb 


Postero-inferior  lobule 


Tuber  valvulae 
Posterior  notch 


Fig.  214.  —  Upper  Surface  of  the  Cerebellum. 


the  bottom  of  the  semilunar  notch,  and  is  only  seen  to  a  very 
small  extent  on  the  upper  surface  of  the  organ.  It  is  a  little 
median  mass  which  is  prolonged  outwards  for  a  short  distance 
round  the  semilunar  notch  in  the  form  of  two  expansions, 
termed  the  alee. 

Lobus  Culminis. — The  culmen  monticuli  constitutes  the 
summit  or  highest  part  of  the  monticulus  of  the  vermis 
superior.  It  is  prolonged  outwards  on  either  side  into  the 
corresponding  hemisphere  as  the  anterior  crescentic  lobule. 
This  is   the  most  anterior  subdivision  on   the  upper   surface 


LOBUS  CACUMINIS 


537 


of  the  hemisphere.     The  two  anterior  crescentic  lobules,  with 
the  culmen  monticuli,  form  the  lobus  culminis  cerebelli. 

Lobus  Clivi. — The  clivus  monticuli  lies  behind  the  culmen, 
from  which  it  is  separated  by  a  distinct  fissure,  and  it  forms 
the  sloping  part  or  descent  of  the  monticulus  of  the  vermis 
superior.      On   each   side  it  is   continuous   with  the  posterior 

Superior  medullary  velum 
Central  lobule  \  Ventricle  iv. 
Superior  peduncle  of  cerebellum       ■    [ 


Middle  peduncle  of  cerebellum 
Inferior  medullary  velum, 


Nodule 


Flocculus 


( licat  horizontal 

fissure         \ 
Postero-inferior  lobule 

Lobulus  gracilis  v        J  I 

Biventral  lobule       !  , 

Pyramid  ! 

Uvula 


Great  horizontal 
fissure 
Lobulus  gracilis 


Biventral  lobule 


Tonsil 
Tuber  valvule 

FlG.  215. — Lower  Surface  of  the  Cerebellum.  The  tonsil  on  the  right  side 
has  been  removed  so  as  to  display  the  inferior  medullary  velum  and 
the  furrowed  band. 

crescentic  lobule  of  the  lateral  hemisphere,  and  the  three  parts 
arc  included  under  the  one  name  of  lobus  clivi. 

The  two  crescentic  lobules  oil   the  upper  surface  of  the  hemisphere  are 
frequently  described  together  as  the  quadrate  lobule. 

Lobus  Cacuminis. — The  folium  cacuminis  forms  the  most 
posterior  part  of  the  vermis  superior,  and  it  bounds  the  great 
horizontal  fissure  superiorly  at  the  posterior  notch.  It  is  a 
single  folium,  the  surface  of  which  may  be  smooth  or  beset 
with  rudimentary  secondary  folia.  It  is  the  connecting  link 
between  the  two postero-superior  lobules  of  the  hemispheres — 
the  three  parts  constituting  thelodus  cacuminis.     As  the  folium 


538 


THE  BRAIN 


cacuminis  is  traced  outwards  into  the  postero-superior  lobule 
of  the  hemisphere,  it  is  found  to  expand  greatly.  The  result 
of  this  is  that  the  postero-superior  lobule  on  each  side  forms 
an  extensive  foliated  district  bounding  the  hinder  part  of  the 
great  horizontal  fissure  above. 

Lobes  on  the  under  surface  of  the  Cerebellum. — The  con- 
nexion between  the  several  parts  of  the  vermis  inferior  and  the 
corresponding  districts  on  the  under  surface  of  the  two  hemi- 
spheres is  not  nearly  so  distinct  as  in  the  case  of  the  vermis 
superior  and  the  lobules  on  the  upper  surface  of  the  hemi- 
spheres. A  groove,  the  sulcus  vallecula,  intervenes  between  the 
vermis  inferior  and  the  hemisphere  on  each  side. 


Culmen 


Central  lobule 


Clivus 


Tuber  valvulae 


Pyramid 


Uvula/ 


Lingula  on  the 
superior  medul- 
lary velum 


Nodule 


Fig.  216. — Mesial  section  through  the  Vermis  of  the  Cerebellum. 
(From  Gegenbaur. ) 

From  behind  forwards  the  following  subdivisions  of  the 
vermis  inferior  may  be  recognised — (i)  the  tuber  valvulae,  (2) 
the  pyramid,  (3)  the  uvula,  and  (4)  the  nodule. 

On  the  under  surface  of  the  hemisphere  there  are  five 
lobules  mapped  out  by  intervening  fissures.  These  are — 
(i)the flocculus,  a  little  lobule  lying  on  the  middle  peduncle 
of  the  cerebellum;  (2)  the  biventral  lobule,  which  lies  immedi- 
ately behind  the  flocculus,  and  is  partially  divided  into  two 
parts  by  a  fissure  which  traverses  its  surface ;  (3)  the  tonsil  or 
amygdala,  a  rounded  lobule,  which  bounds  the  vallecula  on 
the  inner  side  of  the  biventral  lobule  ;  (4)  the  poster o-inferior 
lobule,  placed  behind  the  biventral  lobule,  and  bounding  the 
great  horizontal  fissure  below. 

These  lobules  of  the  hemispheres,  with  the  corresponding 
portions  of  the  vermis  inferior,  constitute  the  lobes  on  the 
under  aspect  of  the  cerebellum. 


ARBOR  VITVE  CEREBELLI  539 

Lobus  Noduli. — The  lobus  noduli  comprises  the  nodule 
and  the  flocculus  of  either  side  with  an  exceedingly  delicate 
connecting  lamina  of  white  matter,  termed  the  i?iferior  medul- 
lary velum. 

The  velum  cannot  be  properly  seen  at  present,  but  it  will  be  exposed  at 
a  later  stage  of  the  dissection. 

Lobus  Uvulae. — The  uvula  is  a  triangular  elevation  placed 
between  the  two  tonsils.  It  is  connected  across  the  sulcus 
valleculas  with  each  tonsil  by  a  low-lying  ridge  of  grey  matter 
scored  by  a  few  shallow  furrows,  and  in  consequence  termed 
the  furrozved  batid.  The  two  tonsils  and  the  uvula  form  the 
lobus  uvulae. 

To  see  the  furrowed  band  it  will  be  necessary  to  remove  the  tonsil  on 
one  side. 

Lobus  Pyramidis. — The  pyramid  is  connected  with  the 
biventral  lobule  on  each  side  by  a  faint  ridge  which  crosses 
the  sulcus  valleculas.  The  term  lobus  pyramidis  is  given  to 
the  three  lobules  which  are  thus  associated  with  each  other. 

Lobus  Tuberis. — The  tuber  valvules,  which  forms  the  most 
posterior  part  of  the  vermis  inferior,  is  composed  of  several 
folia,  which  run  directly  into  the  postero-inferior  lobule  on 
each  side.  The  three  parts  of  the  lobus  tuberis  are  thus  linked 
together.  The  postero-inferior  lobule  is  traversed  by  two, 
or  it  may  be  three,  curved  fissures.  The  most  anterior  of 
these  cuts  off  a  narrow,  curved  strip  of  cerebellar  surface 
called  the  lobulus  gracilis. 

Dissection. — A  mesial  section  should  now  be  made  through  the  vermis 
of  the  cerebellum  and  the  two  medullary  vela  into  the  cavity  of  the  fourth 
ventricle.  When  the  two  parts  of  the  cerebellum  are  drawn  slightly 
asunder,  a  view  of  the  fourth  ventricle  is  obtained  ;  further,  the  connexions 
of  the  two  medullary  vela  and  the  arrangement  of  the  peduncles  of  the 
cerebellum  can  be  more  clearly  understood. 

Arbor  Vitas  Cerebelli. — The  cut  surface  of  the  cerebellum 
presents  a  very  characteristic  appearance.  The  grey  matter 
on  the  surface  stands  out  distinctly  from  the  white  matter  in 
the  interior.  Further,  the  complete  manner  in  which  the 
surface  is  cut  up  by  the  fissures  and  sulci  into  secondary  and 
tertiary  folia  is  seen.  The  central  mass  of  white  matter  in 
the  median  lobe  or  worm  is  termed  the  corpus  trapezoides. 
From  tliis,  main  prolongations  pass  into  the  various  lobules, 
and  these  give  off  branches  so  as  to   supply  each  folium  with 


54o  THE  BRAIN 

a.  central  white  stem  or  core.  The  term  arbor  vitcc  is  applied 
to  the  appearance  which  consequently  results  when  a  section 
is  made  through  the  cerebellum. 

Cerebellar  Peduncles. — These  are  three  in  number  on 
each  side — viz.,  the  middle,  the  superior,  and  the  inferior. 
They  are  all  directly  connected  with  the  white  medullary 
centre  of  the  cerebellum,  and  are  composed  of  fibres  which 
emerge  from  or  enter  the  white  central  substance  of  the 
organ. 

The  middle  peduncle  is  much  the  largest  of  the  three.  It 
is  formed  by  the  transverse  fibres  of  the  pons,  and  it  enters 
the  cerebellar  hemisphere  on  the  outer  side  of  the  other  two. 
The  lips  of  the  anterior  part  of  the  great  horizontal  fissure 
are  separated  widely  from  each  other  to  give  it  admission. 
Within  the  cerebellar  hemisphere  its  fibres  are  distributed  in 
two  great  bundles.  Of  these,  one,  composed  of  the  upper 
transverse  fibres  of  the  pons,  radiates  out  in  the  lower  part  of 
the  hemisphere ;  whilst  the  other,  consisting  of  the  lower 
transverse  fibres  of  the  pons,  spreads  out  in  the  upper  part  of 
the  hemisphere. 

The  inferior  peduncle  is  simply  the  restiform  body  of  the 
medulla.  Leaving  the  back  of  the  medulla  it  turns  sharply 
backwards  and  enters  the  cerebellum  between  the  other  two 
peduncles. 

The  superior  peduncles  are  composed  of  fibres  which  for 
the  most  part  come  from  the  corpus  dentatum  of  the  cerebellar 
hemisphere.  As  they  issue  from  the  cerebellum,  each 
peduncle  lies  close  to  the  inner  side  of  the  corresponding 
middle  peduncle.  They  then  proceed  upwards  towards  the 
inferior  pair  of  quadrigeminal  bodies.  At  first  they  form  the 
lateral  boundaries  of  the  upper  part  of  the  fourth  ventricle, 
but  they  converge  as  they  ascend  on  the  dorsal  aspect  of  the 
pons  Varolii,  so  that  ultimately  they  come  to  overhang  that 
cavity  and  enter  into  the  formation  of  its  roof.  They  dis- 
appear under  cover  of  the  quadrigeminal  bodies,  and  their 
course  in  the  mesencephalon  has  already  been  described. 

Medullary  Vela. — The  medullary  vela  are  closely  associated 
with  the  peduncles.  They  consist  of  two  thin  laminae  of 
white  matter  which  are  projected  out  from  the  white  central 
core  of  the  cerebellum.  The  superior  medullary  velum,  or 
valve  of  Vieussens,  stretches  across  the  interval  between  the 
two  superior  cerebellar  peduncles,  with  the  inner  margins  of 


FLOOR  OF  THE  FOURTH  VENTRICLE      54 t 

which  it  is  directly  continuous.  It  is  triangular  in  form,  and 
when  traced  downwards  it  is  seen  to  be  carried  with  the 
superior  peduncles  into  the  white  matter  of  the  cerebellum. 
Spread  out  on  its  dorsal  surface  is  the  tongue-shaped  prolonga- 
tion of  grey  matter  from  the  cortex  of  the  cerebellum,  which 
is  termed  the  lingula,  and  issuing  from  its  substance  close  to 
the  inferior  quadrigeminal  bodies  are  the  two  trochlear  nerves. 

The  inferior  medullary  velum  is  somewhat  more  complicated 
in  its  connexions.  It  presents  the  same  relation  to  the 
nodule  that  the  superior  velum  presents  to  the  lingula.  It  is 
a  wide  thin  lamina  of  white  matter — so  thin  that  it  is 
translucent — which  is  prolonged  out  from  the  white  centre 
of  the  cerebellum  above  the  nodule.  From  the  nodule  it 
stretches  outwards  to  the  flocculus,  thereby  bringing  these 
two  small  portions  of  the  cerebellum  into  association  with 
each  other.  Where  it  issues  from  the  white  matter  of  the 
cerebellum,  it  might  almost  be  said  to  be  in  contact  with  the 
superior  medullary  velum,  but  as  the  two  laminae  are  traced 
forwards  they  diverge  from  each  other :  the  superior  velum  is 
carried  upwards  between  the  superior  peduncles  of  the  cere- 
bellum, whilst  the  inferior  medullary  velum  turns  downwards 
round  the  nodule,  and  ends  in  a  slightly  thickened  free 
crescentic  edge.  The  cavity  of  the  fourth  ventricle  is  carried 
backwards  between  the  two  vela,  which  form  a  tent-like  roof 
for  it. 

Fourth  Ventricle. — This  cavity  is  somewhat  rhomboidal 
in  form.  Below,  it  tapers  to  a  point  and  becomes  continuous 
with  the  central  canal  of  the  cord ;  above,  it  narrows  in  a 
similar  manner  and  is  continued  into  the  aqueduct  of  Sylvius. 
The  posterior  wall  is  called  the  roof.  The  anterior  wall  is 
termed  the  floor,  and  is  formed  by  the  dorsal  surface  of  the 
medulla  and  of  the  pons.  On  either  side  a  narrow  pointed 
prolongation  of  the  ventricular  cavity  is  carried  outwards  from 
its  widest  part  round  the  upper  part  of  the  corresponding 
restiform  body.  This  is  termed  the  lateral  recess  (Fig.  208, 
p.  526).  Looking  into  the  cavity  between  the  two  portions 
of  the  mesially  divided  cerebellum,  the  lateral  recess  is  very 
apparent. 

Floor  of  the  Fourth  Ventricle. — In  its  lower  part  the  floor 
of  the  fourth  ventricle  is  formed  by  the  dorsal  surface  of  the 
open  part  of  the  medulla,  whilst  in  its  upper  part  it  is  formed 
by   the   dorsal   surface   of  the  pons    Varolii.      The   area    thus 


542  THE  BRAIN 

constituted  is  distinctly  lozenge-shaped,  its  widest  part  being 
opposite  the  inferior  peduncles  of  the  cerebellum.  Further, 
it  presents  definite  lateral  boundaries.  Thus,  below,  it  is 
bounded  on  either  side  by  the  clava,  the  cuneate  tubercle,  and 
the  restiform  body  ;  whilst  above,  the  lateral  limit  is  formed  by 
the  superior  cerebellar  peduncle.  A  thick  layer  of  grey  matter, 
continuous  with  that  surrounding  the  central  canal  of  the  cord, 
is  spread  out  like  a  carpet  over  the  ventricular  floor. 

The  floor  of  the  fourth  ventricle  is  divided  into  two 
symmetrical  and  lateral  portions  by  a  median  groove.  At  the 
lower  narrow  end,  between  the  two  clavae,  it  receives  the 
name  of  the  calamus  scriptorius,  from  its  fancied  resemblance 
to  the  point  of  a  pen.  Crossing  each  half  of  the  floor  at  its 
widest  part  are  several  transverse  bundles  of  fibres  termed 
the  strice  acusticoe.  They  emerge  from  the  mesial  groove,  and 
they  are  carried  outwards  over  the  restiform  body.  The 
striae  acusticae  divide  each  lateral  half  of  the  ventricular  floor 
into  an  upper  and  a  lower  portion,  which  very  nearly 
correspond  to  the  subdivisions  of  this  area  formed  by  the 
medulla  and  the  pons.  On  the  lower  medullary  district  a 
small  triangular  depression,  placed  immediately  below  the 
striae  acusticae,  catches  the  eye.  This  is  termed  the  fovea 
inferior.  It  is  shaped  somewhat  like  an  arrow-head.  The 
apex  or  point  looks  towards  the  striae,  whilst  the  lateral  angles 
of  the  base  are  prolonged  downwards  in  the  form  of  diverging 
grooves.  Of  these,  the  inner  groove  runs  towards  the  opening 
of  the  central  canal  at  the  calamus  scriptorius,  whilst  the 
outer  groove  runs  towards  the  lateral  boundary  of  the  floor. 
In  this  manner  the  portion  of  the  floor  which  lies  below  the 
striae  acusticae  is  mapped  out  into  three  triangular  areas. 
The  mesial  subdivision  is  slightly  elevated,  and  is  termed  the 
trigonum  hypoglossi,  because  subjacent  to  the  inner  part  of  this 
area  is  the  nucleus  of  origin  of  the  hypoglossal  nerve.  The 
intermediate  area  between  the  diverging  grooves  which  proceed 
from  the  base  of  the  fovea  inferior  is  the  trigonum  vagi,  so  called 
because  the  vagus  and  glosso-pharyngeal  nuclei  lie  subjacent 
to  it.  The  external  area  is  the  trigonum  acustici.  The  base 
of  this  area  is  directed  upwards  and  runs  continuously  into 
an  eminence,  the  acustic  tubercle,  over  which  the  striae  acusticae 
pass.  Subjacent  to  this  region  of  the  floor  of  the  ventricle 
lies  the  chief  nucleus  of  termination  of  the  vestibular  part  of 
the  auditory  nerve. 


ROOF  OF  THE  FOURTH  VENTRICLE   543 

Separating  the  base  of  the  trigonum  vagi  from  the  margin  of  the  clava 
there  is  a  narrow  lanceolate  strip  of  the  floor  of  the  fourth  ventricle  to 
which  the  name  of  area  post lre ma  has  been  given  (Retzius). 

On  the  part  of  the  floor  of  the  ventricle  which  lies  above 
the  striae  acusticae,  and  which  corresponds  to  the  dorsal 
surface  of  the  pons,  there  is  also  a  slight  depression.  This  is 
termed  the  fovea  superior.  Between  it  and  the  median  groove 
there  is  a  marked  prominence,  termed  the  eminentia  teres. 
Inferiorly,  this  elevation  passes  downwards  and  becomes 
continuous  with  the  trigonum  hypoglossi ;  whilst  above  it  is 
carried  upwards  towards  the  opening  of  the  aqueduct  of 
Sylvius.  In  both  directions  it  becomes  gradually  less 
prominent,  but  still  it  forms  a  distinct  elongated  elevation 
which  stretches  along  the  whole  length  of  the  median  groove. 
It  is  termed  the  fasciculus  teres.  Proceeding  upwards  from 
the  fovea  superior  to  the  opening  of  the  Sylvian  aqueduct 
there  is  a  shallow  depression,  termed  the  locus  cceruleus. 
When  the  ependyma  is  scraped  away  from  the  surface  of  this 
part  of  the  floor,  some  dark  pigmented  substance,  termed  the 
substantia  ferruginea,  will  be  exposed. 

Roof  of  the  Fourth  Ventricle. — In  its  upper  part  the  roof  of 
the  fourth  ventricle  is  formed  by  the  superior  medullary  velum 
as  it  stretches  across  between  the  two  superior  cerebellar  ped- 
uncles, and  also  to  some  extent  by  the  approximation  of  these 
peduncles  themselves  as  they  approach  the  mesencephalon. 

In  its  lower  part  the  roof  of  the  ventricle  is  exceedingly 
thin,  and  is  not  all  formed  of  nervous  matter.  The  inferior 
medullary  velum  enters  into  its  formation,  and  where  this  fails 
the  epithelial  lining  of  the  cavity,  supported  by  pia  mater,  is 
carried  downwards  towards  the  lower  lateral  boundaries  of 
the  ventricle.  At  the  lowest  part  of  the  calamus  scriptorius, 
and  also  along  each  lateral  boundary,  a  thin  lamina  of  white 
matter  is  carried  for  a  short  distance  over  the  epithelial  roof. 
The  small  lamina  at  the  calamus  scriptorius  overhangs  the 
opening  of  the  central  canal,  and  is  termed  the  obex.  The 
lamina  in  relation  to  the  lateral  boundary  of  the  ventricle  is 
more  extensive,  and  is  called  the  ligula.  It  begins  on  the 
clava,  and  passes  upwards  along  the  cuneate  tubercle  to  the 
restiform  body.  On  the  surface  of  this  it  turns  outwards  so 
as  to  bound  the  lateral  recess  below,  and  in  some  cases  it  may 
be  seen  to  become  continuous  round  the  extremity  of  the 
lateral  recess  with  the  inferior  medullary  velum. 


544  THE  BRAIN 

A  short  distance  above  the  calamus  scriptorius  there  is  an 
aperture  in  the  epithelial  roof  of  the  fourth  ventricle,  by  means 
of  which  the  cavity  of  the  ventricle  communicates  with  the 
subarachnoid  space.  This  opening  is  termed  the  foramen  of 
Magendie.  There  is  also  an  aperture  of  a  similar  character 
in  the  epithelial  roof  of  each  lateral  recess. 

Two  choroid  plexuses,  one  on  either  side  of  the  mesial 
plane,  invaginate  the  roof  of  the  fourth  ventricle  in  such  a 
way  that  they  appear  to  lie  within  the  cavity.  Offshoots 
from  these  likewise  intrude  into  the  lateral  recesses. 

Dissection. — The  dissector  should  now  introduce  his  fingers  into  the 
great  horizontal  fissure  of  the  right  half  of  the  cerebellum,  and  gently 
tear  the  upper  part  of  this  side  of  the  organ  away  from  the  lower  part. 
By  this  proceeding  the  manner  in  which  the  peduncles  enter  the  white 
medullary  centre,  and  also  to  some  extent  the  general  distribution  of 
their  fibres,  will  be  seen. 

Both  portions  of  the  cerebellum  should,  in  the  next  place,  be  removed 
by  cutting  through  the  peduncles  at  the  points  where  they  enter  the 
central  white  matter.  A  horizontal  section  may  then  be  made  through 
the  left  half  of  the  organ,  rather  nearer  its  upper  surface  than  its  lower 
surface.     This  will  reveal  the  corpus  dentatum. 

Corpus  Dentatum  of  the  Cerebellum. — This  is  a  collection 
of  grey  matter,  embedded  in  the  white  medullary  centre  of 
the  lateral  hemisphere  of  the  cerebellum,  which  presents  an 
appearance  very  similar  to  that  of  the  inferior  olivary  nucleus  of 
the  medulla.  It  is  a  thin  lamina  of  grey  matter,  which  appears 
on  section  as  a  wavy  line  folded  upon  itself,  so  as  to  form 
a  crumpled  grey  capsule  with  an  open  mouth  towards  the 
mesial  plane.  The  greater  number  of  the  fibres  which  build 
up  the  superior  cerebellar  peduncle  issue  from  its  mouth. 

There  are  other  smaller  isolated  nuclei  of  grey  matter  in  the  white 
medullary  centre  of  the  cerebellum,  but  these  cannot,  as  a  rule,  be 
demonstrated  in  a  specimen  obtained  in  the  dissecting-room.  They  lie 
nearer  the  mesial  plane. 

Dissection. — A  series  of  transverse  sections  should  now  be  made 
through  the  pons  Varolii  and  the  medulla,  in  order  that  something  of 
their  internal  structure  may  be  learned.  The  structure  of  the  medulla 
is  briefly  described  at  p.  529. 

Internal  Structure  of  the  Pons  Varolii. — When  transverse  sections 
are  made  through  the  pons,  it  is  seen  to  consist  of  two  well-defined  parts, 
viz.,  a  ventral  and  a  dorsal.  Broadly  speaking,  the  ventral  part  corre- 
sponds to  the  pyramidal  parts  of  the  medulla,  and  the  pedal  parts  of 
the  crura  cerebri  ;  whilst  the  dorsal  part  corresponds  to  the  formatio 
reticularis  of  the  medulla  and  the  tegmental  part  of  the  crura  cerebri. 

The  ventral  part  of  the  pons  is  the  larger  of  the  two  subdivisions.  It 
is  composed  of  a  large  number  of  transverse  bundles  of  fibres,  through 


INTERNAL  STRUCTURE  OF  PONS  VAROLII      545 


the  midst  of  which  coarse  longitudinal  bundles  of  fibres  proceed  down- 
wards from  the  crustae  of  the  crura  cerebri  to  form  in  the  medulla  the  two 
pyramids.  Scattered  amongst  these  transverse  and  longitudinal  bundles 
of  fibres,  and  filling  up  the  interstices  between  them,  we  have  a  large  amount 
of  grey  matter  termed  the  nuclei pontis.  Of  the  transverse  fibres  two  distinct 
sets  may  be  recognised,  viz.,  the  superficial  transverse  fibres,  through  the 
midst  of  which  the  pyramidal  bundles  are  prolonged,  and  a  deeper  set  termed 
the  corpus  trapezoides.  The  superficial  transverse  fibres  traverse  the  entire 
thickness  of  the  ventral  part  of  the  pons,  and  on  each  side  pass  into  the 
corresponding  middle  peduncle  of  the  cerebellum.  The  trapezial  fibres 
lie  behind  the  pyramidal  bundles  in  the  boundary  line  between  the  dorsal 
and  ventral  parts  of  the  pons,  but  encroaching  considerably  into  the  ground 


Valve  of  Vieussens 

Ventricle  iv. 

Mesencephalic  root  of  fifth  nerve 

Posterior  longitudinal 
bundle 


Formatio  reticularis  -t 


Nucleus  of 
lateral  fillet 


Trigeminal 


nerve    -^/j 


Grey  matter  on  floor 
/  of  ventricle  iv. 

Superior  cerebellar 
peduncle 

Lateral  fillet 

Commencing  decus- 
sation of  superior 
cerebellar  peduncle 

Mesial  fillet 


Transverse 
fibres  of 
pons 


f 


Pyramidal  bundles 

FlG.  i\-j. — Transverse  section  through  the  upper  part  of  the  Pons  Varolii 

of  the  Oransc. 


of  the  former.  They  are  only  seen  in  the  lower  part  of  the  pons,  and  they 
pass  into  the  lateral  fillet.  They  take  origin  in  the  terminal  nucleus  of  the 
cochlear  division  of  the  auditory  nerve. 

The  dorsal  or  tegmental  part  of  the  pons  is  for  the  most  part  formed 
of  a  prolongation  upwards  of  the  formatio  reticularis  of  the  medulla. 
Superiorly  it  is  carried  into  the  tegmental  parts  of  the  crura  cerebri. 
It  is  divided  into  two  lateral  parts  by  a  mesial  raphe  continuous  below 
with  the  raphe  of  the  medulla  and  above  with  the  raphe  of  the  tegmental 
part  of  the  mesencephalon,  whilst  over  its  dorsal  surface  is  spread  a 
thick  layer  of  grey  matter  which  belongs  to  the  upper  part  of  the  floor 
of  the  fourth  ventricle.  In  transverse  sections  through  the  pons  a  dark 
spot  in  the  outer  part  of  this  indicates  the  position  of  the  substantia 
ferruginea. 

lour  strands  of  longitudinal   fibres  are  seen  on  each  side  in  transverse 
sections  through   the  dorsal   part  of  the  pons.      These  are  (i)  the  mesial 
fillet,  (2)  tin-  Lateral  fillet,  (3)  the  posterior  longitudinal  bundle,  and  (4)  the 
superior  <  :erebellar  peduncle. 
VOL.  11 — 35 


546  THE  BRAIN 

The  mesial  fillet  assumes  in  the  pons  a  ribbon-shaped  form.  It  is  placed 
between  the  ventral  part  of  the  pons  and  the  formatio  reticularis  of  the 
dorsal  part. 

The  lateral  fillet,  largely  composed  of  fibres  derived  directly  or  indirectly 
from  the  corpus  trapezoides,  is  seen  in  the  upper  part  of  the  pons  sweeping 
round  the  outside  of  the  superior  cerebellar  peduncle  so  as  to  gain  the 
surface. 

The  posterior  longitudinal  bundle  is  much  more  distinct  than  it  is 
lower  down  in  the  medulla.  It  has  separated  itself  more  completely 
from  the  longitudinal  fibres  of  the  formatio  reticularis,  and  it  is  now  seen 
close  to  the  mesial  plane  immediately  subjacent  to  the  grey  matter  of 
the  floor  of  the  fourth  ventricle. 

The  superior  cerebellar  peduncle  in  transverse  sections  presents  a  semi- 
lunar outline.  It  occupies  a  lateral  position  in  the  dorsal  part  of  the 
pons,  and  gradually  sinks  deeply  into  its  substance,  although  it  does  not 
become  completely  submerged  until  it  reaches  the  mesencephalon. 

The  superior  olive  is  a  small  isolated  clump  of  grey  matter  which 
is  embedded  in  the  dorsal  part  of  the  pons  in  the  path  of  the  corpus 
trapezoides. 


MEATUS  AUDITORIUS  EXTERNUS  547 


THE  AUDITORY  APPARATUS, 

The  organ  of  hearing  admits  of  a  very  natural  subdivision 
into  three  parts,  viz.,  the  external,  the  middle,  and  the 
internal  ear.  The  external  ear  consists  of  the  pinna  and 
the  external  auditory  meatus.  The  pinna  collects  the  waves 
of  sound,  and  is,  comparatively  speaking,  of  subsidiary  im- 
portance in  man,  although  it  is  highly  developed  and  of 
considerable  service  in  some  of  the  lower  animals.  The 
external  auditory  meatus  is  a  passage  which  leads  inwards 
to  the  membrana  tympani  from  the  bottom  of  the  concha. 
The  middle  ear  is  a  narrow  chamber  termed  the  tympanum 
or  drum  of  the  ear.  It  is  interposed  between  the  external 
auditory  passage  and  the  internal  ear  or  labyrinth,  and  its 
outer  wall  is  formed  by  the  membrana  tympani.  Stretch- 
ing across  the  cavity  of  the  tympanum,  from  its  outer  to 
its  inner  wall,  there  is  a  chain  of  three  minute  bones  called 
the  auditory  ossicles.  The  i?iternal  ear  or  labyrinth  is  the 
essential  part  of  the  organ.  It  consists  of  a  complicated 
system  of  cavities  in  the  densest  part  of  the  petrous  portion 
of  the  temporal  bone.  These  cavities  contain  fluid  called 
perilymph,  and  also  a  membranous  counterpart  of  the  bony 
chambers  called  the  membranous  labyrinth.  Within  the 
latter  there  is  fluid  termed  endolymph. 

Dissection. — In  a  temporal  bone  to  which  the  pinna  is  still  attached 
the  squamous  portion  should  be  removed  by  a  horizontal  saw-cut  at  the 
level  of  the  posterior  root  of  the  zygoma.  With  the  chisel  and  bone 
forceps  the  roof  and  anterior  wall  of  the  auditory  passage  should  then  be 
taken  away  piecemeal,  until  a  good  view  is  obtained  of  the  outer  surface  of 
the  membrana  tympani. 

Meatus  Auditorius  Externus. — The  pinna  has  already 
been  described  (p.  269).  The  external  meatus,  measured 
from  the  bottom  of  the  concha  to  the  membrana  tympani,  is 
about  one  inch  in  length.  It  consists  of  an  outer  part  com- 
posed of  cartilage  and  fibrous  tissue  and  about  8  mm.  long; 
and  an  inner  part,  about  16  mm.  long,  the  walls  of  which  are 
formed  of  bone.  It  does  not  present  a  uniform  diameter,  being 
widest  at  its  entrance  and  narrowest  at  a  point  in  its  osseous 
portion  called  the  isthmus,  which  is  situated  about  5  mm.  from 


54§ 


THE  AUDITORY  APPARATUS 


the  membrana  tympani.  As  the  tube  passes  from  the  surface 
inwards  it  describes  a  gentle  sigmoid  curve,  but  its  general 
direction  is  inwards  with  a  slight  inclination  forwards.  The 
skin  lining  the  cartilaginous  portion  is  abundantly  furnished 
with  ceruminous  glands,  and  is  also  provided  with  outwardly- 
directed  hairs,  which  tend  to  prevent  the  entrance  of  dust. 
The  cutaneous  lining  of  the  osseous  part,  which  is  thin  and 
tightly  adherent  to  the  subjacent  periosteum,  is  destitute  of 


Mastoidal  antrum         Aqueduct  of  Fallopius 


Pyramid 

Iter  chordae 
posterius 

Groove  for 

membrana 

tympani 


Internal 
auditory 
meatus 

Cochlea 


'-■? 


h 


Canal  for  Jacobson's  nerve 

Fig.  218.  — Coronal  section  of  the  Right  Temporal  Bone  passing  through  the 
external  and  the  internal  auditory  meatuses. 

hairs,  and  glands  are  for  the  most  part  absent.  The  cutaneous 
lining  of  the  meatus  is  continued  in  the  form  of  an  exceedingly 
delicate  layer  over  the  outer  surface  of  the  membrana  tympani. 

If  the  subject  is  slightly  decomposed  the  cuticular  lining  of  the  meatus 
may  be  drawn  out  entire,  like  the  finger  of  a  glove,  and  the  epidermal 
covering  of  the  membrana  tympani  is  thus  demonstrated. 

Dissection. — The  tympanic  cavity  can  be  most  conveniently  opened  for 
inspection  by  the  removal  of  its  roof.  The  roof  is  formed  by  a  thin  scale 
of  bone  (tegmen  tympani)  which  extends  beyond  the  limits  of  the  tympanum 
and  covers  in  the  canal  for  the  tensor  tympani  in  front  and  the  mastoidal 
antrum  behind.  An  opening  should  be  made  through  the  tegmen 
tympani,  immediately  external  to  the  elevation  formed  by  the  superior  semi- 


MASTOIDAL  ANTRUM 


549 


circular  canal,  and  about  three-eighths  of  an  inch  in  front  of  the  superior 
border  of  the  petrous  bone.  This  will  open  into  the  mastoidal  antrum. 
The  opening  can  then  be  cautiously  enlarged  with  the  chisel  and  bone  forceps 
until  the  whole  of  the  tegmen  tympani  is  picked  away  piecemeal.  The 
roof  of  the  internal  auditory  meatus  should  also  be  carefully  removed  with 
mallet  and  chisel.  The  mastoidal  antrum,  the  tympanum  with  its  contents, 
the  osseous  portion  of  the  Eustachian  tube,  the  tensor  tympani  muscle,  and 
the  auditory  and  facial  nerves  are  now  displayed. 

Mastoidal    Antrum. — This    is    a    recess    or    air-chamber 
in  the  petrous  bone  with  a  diameter  of  about  one-third  of  an 


Osseous  part  of  meatus 


Recessus 

epitympanicus 

Malleus 

Cochlea 

Tympanum. 

Membrana 

tympani 

Internal  carotid 
artery 


Crus  antihelicis 
inferior 

Cymba  conchae 
Crus  helicis 


Cartilaginous 
part  of  meatus 
Cavum  concha; 


Lower  boundary 
of  incisura 
intertragica 


FlG.  219. — Vertical  transverse  section  through  the  Right  Ear  :  anterior  half 
of  section  viewed  from  behind.      (Howden.  1 


inch.  It  is  placed  behind  the  tympanum,  and  communicates 
by  a  relatively  large  opening  with  the  upper  part  of  that 
cavity.  From  the  surface  of  the  skull  it  lies  at  a  depth  of 
about  half  an  inch,  but  in  the  child  it  is  placed  much  more 
superficially.  It  is  lined  by  mucous  membrane,  which  is 
continuous  with  the  lining  membrane  of  the  tympanum.  The 
mastoid  process  is  also  occupied  by  air-cells.  These  com- 
municate with  the  mastoidal  antrum,  and  are  lined  with 
mucous  membrane.  The  extent  to  which  the  mastoid  pro- 
cess is  hollowed  out  by  air-cells  varies  much  in  different 
individuals.  In  all  cases  it  is  necessary  to  bear  in  mind  the 
intimate  relation  of  the  mastoid  process  and  its  contained 
cells  with  the  lateral  sinus. 


55° 


THE  AUDITORY  APPARATUS 


Tympanic  Cavity  or  Middle  Ear. — The  tympanum  is  a 
small  chamber  filled  with  air,  which  is  placed  between  the 
bottom  of  the  meatus  externus  and  the  internal  ear  or  laby- 
rinth. Behind,  it  communicates  by  a  relatively  large  orifice 
with  the  mastoidal  antrum  and  air-cells ;  whilst  in  front,  the 
Eustachian  tube  opens  into  it  and  brings  it  into  connexion 
with  the  cavity  of  the  pharynx.  It  contains  the  chain  of 
auditory  ossicles  which  cross  from  its  outer  to  its  inner 
wall,  and  it  is  lined  by  delicate  mucous  membrane. 

The  vertical  depth  and  the  antero-posterior  length  of  the 
tympanic  cavity  is  about  half  an  inch  in  each  case.  Its 
width,  however,  from  side  to  side,  is  not  more  than  a  sixth  of 

an  inch,  and  as  both  its  outer  and 
inner  walls  bulge  into  the  cavity,  its 
width  in  the  centre  is  thereby  still 
further  reduced.  The  tympanic 
cavity  consists  of  (i)  an  upper  part, 
which  extends  upwards  beyond  the 
level  of  the  membrana  tympani, 
and  to  which  the  term  recessus 
epitympanicus  is  applied;  and  (2) 
Schematic  vertical  ^}ie  ty??ipanum  proper,  which  lies 
irough    the    Tym-    ,     ,  .  ,.    .    ,     "f       ,       .  .  , 

below,  immediately  to  the  inner  side 

of  the  membrana  tympani.  The 
tympanic  cavity  presents  for  examin- 
ation a  roof  and  a  floor,  with  four 
walls,  viz.,  anterior,  posterior,  ex- 
ternal, and  internal. 

The  roof  is  composed  of  a  thin 
plate  of  bone  termed  the  tegmeti  tympani.  This  separates  it 
from  the  cranial  cavity.  In  chronic  inflammatory  conditions 
of  the  middle  ear  an  extension  of  the  inflammatory  process  to 
the  meninges  of  the  brain  must  always  be  guarded  against. 

The  floor  is  narrow,  and  is  also  formed  by  a  thin  osseous 
lamina,  which  is  interposed  between  the  tympanum  and  the 
jugular  fossa,  which  lodges  the  internal  jugular  vein.  An 
extension  of  an  inflammatory  condition  of  the  middle  ear  in 
this  direction,  therefore,  might  lead  to  thrombosis. 

The  posterior  wall  presents,  in  its  upper  part,  the  opening 
which  leads  from  the  recessus  epitympanicus  into  the 
mastoidal  antrum,  and  below  this,  close  to  the  inner  wall,  a 
small  hollow  conical  projection  termed  the  pyramid.     This  is 


Fig.  220. 
section    thro 
panum.      (From  Testut. ) 

1.  External  meatus. 

2.  Tympanic   cavity  (the  upper 

"2"  is  in  the  recessus  epi- 
tympanicus). 

3.  Promontory  or  inner  wall. 

4.  Membrana  tympani. 


TYMPANIC  CAVITY  OR  MIDDLE  EAR       551 


perforated  on  its  summit,  and  the  aperture  leads  into  a  canal 
which  curves  backwards  and  then  downwards  until  it  finally 
opens  into  the  lower  part  of  the  last  stage  of  the  Fallopian 
aqueduct.  This  curved  canal  lodges  the  stapedius  muscle, 
the  delicate  tendon  of  which  enters  the  tympanic  cavity 
through  the  aperture  on  the  summit  of  the  pyramid.  On  the 
outer  side  of  the  pyramid  is  the  aperture  on  the  posterior 
wall  through  which  the  chorda  tympani  nerve  enters  the 
tympanum. 

Mastoid  antrum 
Recessus  epitympanicus 


Aqueduct  of  Fallopiu 


Tegme 


Fenestra 

Canal  for 
tensor  tympani 

Processus 
cochleariformis 

Promontory 

Eustachian  tube 

Foramen  for 
Jacobson's  nerve 


Pyramid 


Fenestra  rotunda 


Course  of  aqueduct  of  Fallopiu^ 


FlG.  221. — Section  through  the  Left  Temporal  Bone  showing  the  Inner 
Wall  of  the  Tympanic  Cavity.      (Howden. ) 

The  anterior  wall  is  narrow,  because  the  inner  and  outer 
walls  become  somewhat  approximated  to  each  other  as  they 
are  traced  forwards.  To  a  large  extent  this  wall  is  deficient,  as 
here  the  tympanic  cavity  is  continued  directly  into  the  osseous 
part  of  the  Eustachian  tube.  Above  this  aperture  is  the  canal, 
in  which  is  lodged  the  tensor  tympani  muscle. 

The  inner  wall  which  intervenes  between  the  tympanum 
and  the  labyrinth  presents  certain  important  points  for  study. 
The  greater  part  of  this  wall  bulges  outwards  into  the  cavity 
in  the  form  of  a  very  evident  elevation  termed  the  promontory. 
Above    the    hinder   part    of  the    promontory  there    is   an    oval 


552 


THE  AUDITORY  APPARATUS 


foramen,  the  long  axis  of  which  is  directed  from  before  back- 
wards. This  is  the  fenestra  ovalis,  an  opening  into  the 
vestibular  part  of  the  labyrinth,  and  it  is  closed  in  the  recent 
state  by  the  footpiece  of  the  stapes,  the  innermost  of  the 
auditory  ossicles.  The  pyramid  on  the  posterior  wall  will  be 
seen  to  lie  immediately  behind  the  fenestra  ovalis.  Above 
the  fenestra  ovalis,  in  the  angle  formed  by  the  meeting  of  the 
roof  and  inner  wall  of  the  tympanum,  and  therefore  in  the 
recessus   epitympanicus,   a  ridge,  arching  from   before  back- 


Recessus  epitympanicus 


Fossa 
incudis 


Iter  chordae 
posterius 


Membrana 

rlaccida 

Anterior  and  pos- 
terior tympano- 
malleolar  folds 
Tendon  of  tensor 
tympani  (cut) 
Handle  of 
malleus 

Membrana 
tympani 

Tympanic  sulcus 


FlG.  222. — Left  Membrana  Tympani  and  Recessus  Epitympanicus  viewed 
from  within.  The  neck  and  head  of  the  malleus  have  been  removed  to 
show  the  membrana  flaccida.      (Howden. ) 


wards,  will  be  seen.  This  is  produced  by  the  aqueduct  of 
Fallopius  bulging  into  the  tympanum.  Its  wall  is  very  thin, 
and  allows  the  white  colour  of  the  facial  nerve  which  is  con- 
tained within  the  canal  to  be  readily  seen.  In  front  of  this 
ridge,  in  the  upper  part  of  the  inner  wall  of  the  tympanum, 
is  the  processus  cochleariformis  supporting  the  tensor  tympani 
muscle.  The  processus  cochleariformis  forms  a  trough  or 
gutter  of  bone  which  runs  backwards  towards  the  anterior  end 
of  the  fenestra  ovalis,  immediately  above  which  it  terminates. 
Here  it  makes  a  sharp  bend,  which  almost  surrounds  the 
tendon  of  the  tensor  tympani,  and  forms  a  pulley  upon  which 


MEMBRANA  TYMPANI 


553 


the  tendon  plays.  Below  the  hinder  end  of  the  promontory 
is  the  fenestra  rotunda^  an  aperture  which,  in  the  macerated 
bone,  leads  into  the  cavity  of  the  cochlea,  but  which  in  the 
recent  state  is  closed  by  a  membrane  which  is  stretched 
across  it,  and  receives  the  name  of  the  secondary  membrane  of 
the  tympanum. 

The  outer  wall  of  the  tympanic  cavity  is  formed  for  the 
most  part  by  the  membrana  tympani. 

Membrana    Tympani. — The    membrana    tympani    is    an 


Recessus 
epitympanicus 

Body  of  incus 

Short  process 

of  incus 

Ligament 

of  incus 


Chorda  tym- 
pani nerve 
Pyramid 


Superior  ligament  of  malleus 

Head  of  malleus 


Anterior  ligament 
of  malleus 


Handle  of  malleus 


Foot  of  stapes 


Tensor  tympani 

Processus 
cochleariformis 
Osseous  part  of 
the  Eustachian 
tube 


FlG.  223. — Left  Membrana  Tympani  and  Chain  of  Tympanic  Ossicles 
seen  from  the  inner  aspect.      (Howden.  1 

elliptical  disc  of  membrane  which  is  stretched  across  the 
bottom  of  the  meatus  auditorius  externus,  so  as  to  form  the 
greater  part  of  the  outer  wall  of  the  tympanum.  It  is  placed 
very  obliquely;  its  lower  and  its  fore  borders  both  incline 
inwards. 

Its  mode  of  attachment  around  the  bottom  of  the  meatus 
is  deserving  of  some  attention.  Here,  there  is  a  ring-like 
ridge  of  bone  very  distinctly  grooved  which  forms,  as  it  were, 
a  frame  in  which  the  membrane  is  set.  But  this  ridge  is 
deficient  above,  and  at  this  point  there  is  a  deep  notch  (the 
notch  of  Rivinusj  between  the  extremities  of  the  bony  ridge. 
This  notch  is  occupied  by  a  portion  of  the  membrane  which 


554 


THE  AUDITORY  APPARATUS 


is  not  so  dense  in  its  texture  (seeing  that  the  fibrous  layer  is 
absent),  and  not  so  tightly  stretched ;  consequently  it  receives 
the  name  of  the  membrana  fiaccida  (Shrapnell's  membrane). 
The  edge  of  that  part  of  the  membrane  which  is  fixed  in  the 
circular  bony  groove  (sulcus  tympanicus)  is  thickened,  and  at 
the  notch  of  Rivinus  it  is  carried  down  in  front  and  behind  the 
membrana  fiaccida  in  the  form  of  two  bands,  called  respectively 
the  anterior  and.  posterior  tympano-malleolar  folds. 

The  membrana  tympani  is  composed  of  three  layers — viz., 
an  outside  cuticular  layer,  an  intermediate  fibrous  lamina, 
and  an  inside  mucous  layer.  The  handle  of  the  malleus  is 
intimately  connected  with  the  fibrous  layer,  and  is  covered 


Membrana  fiaccida 
Anterior  tympano- 
malleolar  fold 


Handle  of  malleus 

Antero-superior 
quadrant 


Anteroinferior  quadrant 


Posterior  tympano- 
malleolar  fold 
Short  process 
of  malleus 
Long  process  of  incus 

Postero-superior 
quadrant 

Postero-inferior 
quadrant 

Cone  of  light 


Fig.  224. — Left  Tympanic  Membrane  as  viewed  from  the  external  auditory 
meatus  during  an  otoscopic  examination.  The  dotted  lines  indicate  the 
manner  in  which  the  tympanic  membrane  is  subdivided  arbitrarily  into 
four  areas  or  quadrants.      (Howden.) 

over  by  the  mucous  layer.  It  draws  the  membrane  inwards 
towards  the  tympanic  cavity,  so  that  the  outer  surface  is 
deeply  concave.  The  deepest  point  of  this  concavity  cor- 
responds with  the  flattened  extremity  of  the  handle  of  the 
malleus,  and  is  termed  the  umbo  or  umbilicus. 


In  examining  the  living  ear  with  a  speculum,  the  surface  of  the  mem- 
brane appears  highly  polished,  and  a  cone  of  light  extends  downwards 
and  forwards  from  the  tip  of  the  handle  of  the  malleus.  A  pair  of  striae 
(Prussak's  striae),  which  correspond  to  the  anterior  and  posterior  tympano- 
malleolar  folds,  extend  from  the  processus  brevis  of  the  malleus  to  the 
margins  of  the  notch  of  Rivinus,  and  thus  map  out  Shrapnell's  membrane. 
The  long  process  of  the  incus  can  be  faintly  seen  through  the  membrana 
tympani,  parallel  to  and  behind  the  handle  of  the  malleus. 


AUDITORY  OSSICLES 


555 


Tympanic  Mucous  Membrane. — The  tympanum  is  lined 
throughout  with  a  thin  mucous  membrane  which  is  continu- 
ous with  the  mucous  membrane  of  the  pharynx.  As  already 
mentioned,  it  forms  the  innermost  layer  of  the  membrana 
tympani,  and  is  prolonged  backwards  into  the  mastoidal 
antrum  and  air-cells.  It  also  covers  the  ossicles  and  invests 
the  tendons  of  the  stapedius  and  tensor  tympani  muscles. 

Auditory  Ossicles. — These  are  termed  the  malleus,  the 
incus,  and  the  stapes. 

The  malleus  presents  a  head, 
a  neck,  a  manubrium  or  handle, 
and  two  processes  termed  re- 
spectively the  processus  brevis 
and  the  processus  gracilis.  The 
head  is  large  and  rounded. 
It  is  directed  upwards,  and 
lies  above  the  level  of  the 
membrana  tympani,  in  the  re- 
cessus  epitympanicus  and  close 
to  the  roof  of  the  tympanum. 
On  its  posterior  aspect  there  is 
a  notch -like  articular  surface 
directed  backwards  for  articula- 
tion with  the  body  of  the  incus. 
The  manubrium  is  attached  to 
the  fibrous  layer  of  the  membrana 
tympani.  The  processus  brevis 
is  '  a  stunted  projection  which 
springs  from  the  root  of  the 
manubrium.  It  is  directed  out- 
wards, and  abuts  against  the 
membrana  tympani  immediately  below  the  membrana  flaccida. 
The  processus  gracilis  is  a  slender  spicule  of  bone  which  is 
directed  forwards,  and  enters  the  Glaserian  fissure.  It  almost 
invariably  breaks  in  detaching  the  malleus  from  the  adult 
skull,  but  it  can  be  easily  preserved  in  the  skull  of  an  infant. 

The  incus  is  shaped  somewhat  like  a  bicuspid  tooth  in 
which  the  fangs  are  very  divergent.  It  presents  a  body  with 
a  long  and  a  short  process.  The  body  is  provided  with  an 
articular  surface  which  looks  forwards  and  articulates  with 
the  head  of  the  malleus.  The  short  process  is  directed  back- 
wards,   and    its   extremity   is   attached   by   ligaments   to    the 


Fig.  225. — Left  Malleus  and  Incus. 
~( After  Helmholtz.) 


Tendon  of  tensor  tympani. 

Handle  of  the  malleus. 

Long  process  of  the  incus. 

Short  process  of  the  incus. 

Processus  gracilis  of  the  malleus.  The 
straight  line  a  b  c  connects  the  ex- 
tremities of  the  two  processes  of  the 
incus  with  the  extremity  of  the 
manubrium  of  the  malleus. 


556 


THE  AUDITORY  APPARATUS 


posterior  wall  of  the  tympanum  near  the  opening  into  the 
mastoidal  antrum.  The  long  process  proceeds  downwards 
and  inwards  in  a  direction  nearly  parallel  to  that  of  the 
manubrium   of  the    malleus,    but    internal,    and   on    a    plane 


Head.      Facet  for 
Neck  incus 


Facet  for    Head 

incus  Processus 

gracilis 


Processus 
brevis 

Manubrium  Manubrium 

A  B 

Fig.  226. — The  Left  Malleus.      (Howden. ) 

A.   Viewed  from  behind.  I!.  Viewed  from  inner  side. 


posterior  to  that  process.  On  its  inferior  extremity,  which 
is  bent  inwards,  there  is  a  small  knob  of  bone  called  the 
processus  lenticularis.  This  articulates  with  the  head  of  the 
stapes. 

The  malleus  and  incus  move  together  on  an  axis  which  is  formed  by 


Articular  surface  for 
head  of  malleus 


Short  process 


Hod  j' 


Processus. 
longus 

Processus 
lenticularis 

Long  process 

A  B 

FlG.  227. — The  Left  Incus.      (Howden.) 

A.   Seen  from  the  fruiit.  B.    Seen  from  the  inner  side. 

the  processus  gracilis  of  the  malleus  and  the  short  process  of  the  incus, 
The  articular  surfaces  of  the  two  bones  are  provided  with  peculiar  catch- 
teeth  which  interlock  when  the  bones  are  performing  their  ordinary 
movements.      When,  however,  force   is  applied  to   the  inner    surface  of 


LIGAMENTS  OF  AUDITORY  OSSICLES 


o5  / 


the  membrana  tympani,  as,  for  instance,  when  the  tympanum  is  inflated 
through  the  Eustachian  tube,  the  malleo-incudal  joint  gapes  and  the 
malleus  moves  by  itself.  Traction  upon  the  attachments  of  the  stapes, 
through  the  incus,  is  thus  obviated. 

The  stapes  is  shaped  like  a  stirrup,  and  presents  a  head 
or  outer  extremity  separated  by  a  slightly  constricted  neck 
from  two  limbs  or  crura  which  join  an  internal  plate  or 
footpiece.  The  head  is  excavated  by  an  articular  cup  for  the 
processus  lenticularis  of  the  incus.  The  crura  are  grooved 
longitudinally  on  their  concave  sides  (sulcus  stapedis).  The 
posterior  cms  is  more  sharply  curved  than  the  anterior 
crus.  The  footpiece  fits  into  the  fenestra  ovalis  and  corre- 
sponds in  its  outline  with  this  aperture.  Its  lower  border  is 
straight,  whilst  its  upper  border  is  curved. 

Ligaments  of  the  Auditory  Ossicles. — In  addition  to  the 
delicate   capsular    ligaments  which  sur- 
round the  joints  between  the  auditory         ^^^^Neck 
ossicles,  there  are  certain  bands   which      (tf\\ — Cms  anterior 

connect  the  bones  to  the  walls  of  the     If i r~Cnis  p°sterior 

tympanum    and   serve   to  restrain   their    ^^^^>Foot.  ]ate 
movements.  (~~  ~~^*C 

In    connexion    with    the    malleus    there    are     Fig.  228. — Left  Stapes, 
(i)   an  anterior  ligament  which  passes  from  its  ( How  den.  1 

fore-part  at  the  root  of  the  processus  gracilis  to 

the  anterior  wall  of  the  tympanum  in  the  neighbourhood  of  the  Glaserian 
fissure  ;  (2)  an  external  ligament  which  extends  from  its  short  process  to 
the  margin  of  the  notch  of  Rivinus  ;  and  (3)  a  superior  ligament  which 
connects  the  head  with  the  roof  of  the  tympanum. 

The  ligament  of  the  incus  binds  the  extremity  of  its  short  process  to  the 
posterior  wall  of  the  tympanum,  whilst  the  annular  ligament  of  the  stapes 
connects  the  margin  of  its  footpiece  to  the  circumference  of  the  fenestra  ovalis. 

Tympanic  Muscles. — These  are  two  in  number,  viz.,  the 
stapedius  inserted  into  the  neck  of  the  stapes,  and  the  tensor 
tympani  inserted  into  the  malleus. 

The  stapedius  occupies  the  interior  of  the  pyramid  and  the 
canal  which  curves  downwards  from  it.  The  delicate  tendon 
of  the  stapedius  enters  the  tympanum  through  the  aperture 
on  the  summit  of  the  pyramid,  and  is  inserted  into  the 
posterior  aspect  of  the  neck  of  the  stapes.  It  is  supplied  by 
a  branch  from  the  facial  nerve. 

The  tensor  tympani  arises  from  the  upper  part  of  the 
cartilage  of  the  Eustachian  tube  and  from  the  contiguous 
part  of  the  great  wing  of  the  sphenoid.       From  this  it  passes 


558  THE  AUDITORY  APPARATUS 

backwards  and  outwards  upon  the  processus  cochleariformis 
and  above  the  osseous  part  of  the  Eustachian  tube.  In  the 
tympanic  cavity  the  tendon  turns  sharply  round  the  extremity 
of  the  processus  cochleariformis  and  proceeds  directly  out- 
wards, from  the  inner  towards  the  outer  wall  of  the  tympanum 
to  its  insertion  into  the  upper  part  of  the  manubrium  of  the 
malleus  on  its  internal  aspect.  The  tensor  tympani  receives 
its  nerve  of  supply  from  the  otic  ganglion. 

Chorda  Tympani  Nerve. — The  chorda  tympani,  which 
traverses  the  tympanic  cavity  in  close  relation  to  the  upper 
part  of  the  membrana  tympani,  is  described  on  p.  407. 

Tympanic  Plexus. — This  has  also  been  previously  de- 
scribed on  p.  314. 

Eustachian  Tube. — The  Eustachian  tube  is  the  passage 
which  brings  the  tympanic  cavity  into  communication  with 
the  pharynx,  and  through  which  air  reaches  the  tympanic 
cavity  and  the  mastoidal  cells.  It  consists  of  an  osseous 
and  a  cartilaginous  portion.  The  osseous  portion  is  abolit  half 
an  inch  in  length.  It  is  widest  at  its  entrance  into  the 
tympanum,  and  narrowest  at  its  other  end.  The  cartilaginous 
poiiion  is  about  an  inch  in  length,  and  has  been  already 
described  on  p.  381. 

Dissection. — A  good  deal  of  the  anatomy  of  the  internal  ear  may  be 
learned  by  chiselling  away  the  surrounding  bone  from  the  harder  walls  of 
the  different  cavities  which  form  the  osseous  labyrinth.  When  this  is 
being  done  the  bone  must  be  held  in  a  vice.  The  dissection  can  best  be 
carried  out  in  the  petrous  bones  of  an  eighth-month  or  a  full-time  foetus. 

Various  sections  should  also  be  made  through  the  macerated  bone. 

Internal  Ear  or  Labyrinth. — The  labyrinth  consists  of  an 
intricate  system  of  cavities  in  the  petrous  part  of  the  temporal 
bone.  They  contain  hollow  membranous  structures  in  con- 
nexion with  which  the  filaments  of  the  auditory  nerve  end. 
We  therefore  recognise  an  osseous  and  a  membranous 
labyrinth. 

The  osseous  labyrinth  is  composed  of  an  intermediate 
chamber  termed  the  vestibule,  behind  which  are  placed  the 
three  semicircular  canals,  whilst  in  front  is  the  cochlea.  All 
these  cavities  communicate  with  each  other.  The  corre- 
sponding membranous  parts  do  not  completely  occupy  the 
osseous  chambers,  and  the  intervening  space  is  filled  writh  a 
fluid  termed  the  perilymph.  The  membranous  labyrinth  also 
contains  a  fluid  which  receives  the  name  of  endolymph. 


VESTIBULE 


559 


Vestibule. — The  vestibule  is  a  small  ovoidal  bony  chamber, 
the  antero-posterior  diameter  of  which  is  about  the  sixth  of 
an  inch  in  length.  It  is  situated  between  the  inner  wall 
of  the  tympanum  and  the  bottom  of  the  internal  auditory 
meatus. 

Into  the  back-part  of  the  vestibule  the  three  semicircular 
canals  open  by  five  round  apertures ;  whilst  in  its  lower 
and  fore  part  is  the  opening  of  the  scala  vestibuli  of  the 
cochlea. 

On  the  outer  wall  is  the  fenestra  ovalis,  which  is  closed 
in  the  recent  state   by  the  delicate   periosteal  lining  of  the 


Fovea  hemi-elliptica 
Crista  vestibuli 
Fovea  hemispherica 


Scala  tympani 
Lamina  spiralis  ossea 
Scala  vestibuli 

Opening  of 
aqueductus  cochleae 

Fenestra  rotunda 


Superior  semi- 
circular canal 


External  semi- 
circular canal 


Posterior  semi- 
circular canal 


Opening  cf  crus  commune 
Opening  of  aqueductus  vestibuli 


FlG.  229. — Interior  of  the  Left  Bony  Labyrinth  viewed  from 
the  outer  aspect.     (How den. ) 

chamber  and  the  footpiece  of  the  stapes.  When  these  parts 
are  removed,  the  vestibule  communicates  directly  through 
this  aperture  with  the  tympanum.  On  the  anterior  part  of 
the  inner  wall  of  the  vestibule  there  is  a  circular  depression, 
termed  the  fovea  hemispherica,  which  is  bounded  behind  by 
a  vertical  ridge,  called  the  crista  vestibuli.  The  bottom  of 
the  fovea  hemispherica  is  perforated  by  some  minute  holes 
which  give  admission  to  filaments  from  the  auditory  nerve. 
On  the  roof  of  the  vestibule  another  depression,  named  the 
fovea  hemi-elliptica,  may  be  seen.  It  is  placed  behind  the 
crista  vestibuli. 

A  small  aperture  placed  on  the  posterior  part  of  the  inner 
wall  likewise  deserves  mention.  It  is  the  mouth  of  the 
ar/ueduclus  vestibuli — a  small   canal  which  leads  backwards  to 


56° 


THE  AUDITORY  APPARATUS 


the  posterior  surface  of  the  petrous  bone,    where   it   opens 
under  the  dura  mater. 

Semicircular  Canals. — These  are  three  bony  canals  or 
tubes  placed  behind  the  vestibule.  They  are  bent  upon 
themselves,  so  that  each  forms  considerably  more  than  half 
a  circle,  and  they  occupy  planes  at  right  angles  to  each  other 
like  three  faces  of  a  cube.  They  are  termed  superior,  pos- 
terior, and  external,  and  they  open  into  the  back  part  of  the 
vestibule  by  five  round  orifices,  the  number  of  openings 
being  thus  reduced  through  the  adjoining  extremities  of  the 
superior  and  posterior  canals  becoming  fused  together  so  as 
to   present   a   common    canal  (crus  commune)  with   a  single 


Superior  semicircular  canal 
with  its  ampulla 


Aqueduct  of 
Fallopius 


Cochlea 

Fenestrarotunda 
Fenestra  ovalis 
Ampulla  of  posterior  semicircular  canal 
Ampulla  of  external  semicircular  canal 


Posterior  semi- 
circular canal 
Crus  commune 


External  semicircular  canal 
Fig.  230. — Left  Bony  Labyrinth  viewed  from  outer  side.      (Howden.) 

orifice.  One  extremity  of  each  canal  where  it  joins  the 
vestibule  becomes  expanded  into  what  is  termed  its  ampulla. 
There  are  thus  three  ampullated  ends. 

The  superior  semicircular  canal  forms  the  highest  part  of 
the  labyrinth,  and  gives  rise  to  a  smooth  elevation  on  the 
anterior  surface  of  the  petrous  bone,  immediately  in  front 
of  its  superior  border.  It  is  vertical,  and  placed  somewhat 
transversely  to  the  long  axis  of  the  petrous  bone.  The 
posterior  semicircular  canal,  which  is  the  longest  of  the  three 
tubes,  is  also  vertical,  and  lies  in  a  plane  parallel  to  the 
posterior  surface  of  the  petrous  bone.  The  external  semi- 
circular canal  is  the  shortest  of  the  tubes,  and  occupies  a 
horizontal  plane. 

Cochlea. — The  cochlea  is  a  tapering  tube  which  is  coiled 


COCHLEA  561 

spirally  for  two  turns  and  a  half  around  a  central  pillar,  termed 
the  modiolus.  The  appearance  produced  is  somewhat  similar 
to  that  of  a  spiral  shell.  The  cochlea  lies  in  front  of  the 
vestibule,  with  its  base  directed  towards  the  bottom  of  the 
internal  auditory  meatus ;  whilst  its  apex  looks  forwards 
and  outwards,  and  comes  into  close  relation  with  the  canal 
for  the  tensor  tympani  muscle. 

The  cochlear  tube  rapidly  diminishes  in  diameter  as  it 
is  traced  towards  the  apex  of  the  cochlea,  and  its  closed 
extremity  is  termed  the  cupola.  The  first  turn  which  it 
takes  around  the  modiolus  produces  the  bulging  on  the 
inner  wall  of  the  tympanum,  which  has  been  described  under 
the  name  of  the  promontory. 

The  modiolus  is  thick  at  the  base,  but  rapidly  tapers 
towards  the  apex.  Its  base  abuts  against  the  bottom  of 
the  internal  auditory  meatus.  It  forms  the  inner  wall  of 
the  cochlear  tube,  and  winding  spirally  round  it  like  the 
thread  of  a  screw  is  a  thin  lamina  of  bone,  termed  the  lamina 
spiralis,  which  partially  subdivides  the  tube  into  two  passages. 

Numerous  minute  canals  traverse  the  modiolus,  and  one  more  con- 
spicuous than  the  others,  the  central  canal  of  the  modiolus,  extends 
along  its  centre.  The  spiral  lamina  is  also  tunnelled  by  small  canals 
in  communication  with  those  in  the  modiolus,  whilst  one,  the  spiral 
canal  of  the  modiolus,  winds  spirally  around  the  central  pillar  in  the 
attached  margin  of  the  spiral  lamina.  All  these  channels  convey 
filaments  from  the  cochlear  division  of  the  auditory  nerve  to  the 
membranous  cochlea,  whilst  the  spiral  canal  lodges  the  ganglion  spirale 
cochlea. 

The  7nembra?wus  cochlear  tube  or  ductus  cochlearis  is  placed 
between  the  free  margin  of  the  spiral  lamina  and  the 
opposite  side  of  the  wall  of  the  cochlear  tube.  The  two 
compartments  of  the  bony  cochlea  are  thus  separated  from 
each  other,  and  they  are  respectively  termed  the  scala 
tympani  and  the  scala  vestibuli.  The  scala  tympani  is  the 
larger  of  the  two.  It  begins  at  the  fenestra  rotunda,  where 
the  secondary  membrane  of  the  tympanum  shuts  it  off  from 
the  tympanic  cavity.  At  the  apex  of  the  cochlea  it  com- 
municates by  means  of  an  aperture,  termed  the  helicotrema, 
with  the  scala  vestibuli.  At  the  base  of  the  cochlea  the  scala 
7>estibuli  communicates  with  the  lower  and  fore  part  of  the 
vestibule.  The  perilymph  therefore,  in  the  semicircular 
canals  and  vestibule,  is  directly  continuous  with  that  in  the 
scala  vestibuli  and  scala  tympani. 

VOL.    II-     30 


562 


THE  AUDITORY  APPARATUS 


It  can  now  be  easily  understood  how  vibrations  of  the  membrana 
tympani  are  communicated  to  the  perilymph  within  the  osseous  laby- 
rinth. The  chain  of  auditory  ossicles  through  the  footpiece  of  the 
stapes  affects  the  perilymph  in  the  vestibule.  The  vibrations  of  the 
perilymph  passing  along  the  scala  vestibuli  into  the  scala  tympani  in 
turn  affect  the  aecondary  membrane  of  the  tympanum  which  is  stretched 
across  the  foramen  rotundum.  With  every  inward  movement  of  the 
membrana  tympani  and  of  the  footpiece  of  the  stapes,  there  is  an  out- 
ward movement  of  the  membrane  of  the  foramen  rotundum  and  vice 
versa.  The  vibrations  of  the  perilymph  affect  the  endolymph  in  the 
membranous   labyrinth,  and  thus  excite  the  terminations  of  the  auditory 


Ductus  endolymphaticus 


Dura 


Vestibule 


Osseous 
cochlea 


Osseous 

semicircular 

canal 


Membranous 

semicircular 

canal 


Stapes 

Fenestra  rotunda 

Aqueductus  cochleae 


Modiolus 


Fig.  231. — Diagram  of  the  Osseous  and  Membranous  Labyrinth. 
(Modified  from  Testut. ) 


U.   Utricle. 


6".   Saccule. 


D.C.  Ductus  cochlearis. 


Membranous  Labyrinth.  —  In  the  vestibule  there  are  two  mem- 
branous sacs  termed  the  utricle  and  the  saccule.  The  zrtricle  occupies 
the  fovea  hemi-elliptica  on  the  wall  of  the  vestibule,  and  lies  above 
and  behind  the  saccule.      Into  it  open  the  membranous  semicircular  canals. 

The  saccule  is  smaller,  and  occupies  the  fovea  hemispherica  on  the  fore- 
part of  the  inner  wall  of  the  vestibule.  It  communicates  by  means  of  a 
short  narrow  tube,  termed  the  canalis  reuniens,  with  the  ductus  cochlearis 
or  membranous  cochlear  tube. 

The  saccule  and  the  utricle  are  only  indirectly  brought  into  communica- 
tion with  each  other. 

A  slender  tube  termed  the  ductus  endolymphatiais  occupies  the  aque- 
ductus vestibuli,  and  divides  into  two  branches  which  pass  respectively  into 
the  saccule  and  the  utricle  (Fig.  231). 

The  ductus  cochlearis,  or  scala  media,  as  we  have  already  noted,  lies 
between  the  two  scala?  of  the  cochlear  tube.  It  ends  blindly  at  each 
extremity,  but  close  to  its  basal  end  it  is  brought  into  communication  with 
the  saccule  by  the  canalis  reuniens. 


THE  EYEBALL  563 


THE   EYEBALL. 

The  eyeball  is  not  perfectly  spherical ;  it  may  be  said  to  be 
composed  of  the  segments  of  two  spheres.  The  anterior  or 
corneal  segment,  forming  only  about  one-sixth  of  the  entire 
eyeball,  possesses  a  shorter  radius  than  the  hinder  or  sclerotic 
segment.  The  anterior  clear  corneal  part  of  the  eyeball 
forms,  therefore,  a  dome-like  bulging  or  prominence  on  the 
front  of  the  globe  of  the  eye.  The  terms  anterior  and 
posterior  pole  are  respectively  applied  to  the  central  points  of 
the  anterior  and  posterior  segments  of  the  eyeball.  The 
imaginary  line  which  joins  these  poles  receives  the  name 
of  the  sagittal  axis,  whilst  another  line  drawn  in  a.  coronal 
direction  around  the  globe  of  the  eye  midway  between  the 
two  poles  so  as  to  divide  the  eyeball  into  two  hemispheres 
is  termed  the  equator.  Imaginary  meridional  lines  are  also 
drawn  between  the  two  poles  so  as  to  cut  the  equatorial  line 
at  right  angles.  In  studying  the  structure  of  the  eyeball  it  is 
necessary  to  have  a  proper  understanding  of  these  terms. 

Dissection  of  the  Eyeball. — A  satisfactory  dissection  of  the  globe  of  the 
eye  can  only  be  made  when  the  eyeball  is  fresh  ;  and  in  the  dissecting- 
room  it  is  often  impossible  to  obtain  suitable  specimens.  This  does  not  in 
reality  matter  very  much,  because  it  is  always  easy  to  procure  eyeballs  of 
the  pig,  sheep,  or  ox,  which  suit  the  purpose  admirably.  It  is  essential, 
however,  that  the  dissector  should  always  complete  his  study  of  the  organ 
by  the  examination  of  a  fresh  human  eyeball  obtained  from  the  post-mortem 
room.  In  point  of  size  and  also  in  other  particulars  the  eyeball  of  the  pig 
more  closely  resembles  the  human  eyeball,  but  it  is  perhaps  better  that  the 
student  should  begin  with  the  eyeball  of  the  ox,  seeing  that  in  it  the 
dissection  can  be  more  easily  carried  out. 

We  shall  suppose  then  that  the  dissector  has  provided  himself  with  six 
eyeballs  obtained  from  oxen.  His  first  duty  is  to  remove  from  these  the 
conjunctiva,  capsule  of  Tenon,  ocular  muscles,  and  fat,  which  adhere  to 
them.  Pinching  up  with  the  forceps  the  conjunctiva  and  capsule  of 
Tenon  close  to  the  corneal  margin,  he  should  snip  through  these  layers 
with  the  scissors  and  divide  them  completely  round  the  edge  of  the  cornea. 
It  is  now  easy  to  strip  all  the  soft  parts  from  the  surface  of  the  sclerotic 
coat,  working  steadily  backwards  towards  the  entrance  of  the  optic  nerve. 
A  little  behind  the  equator  of  the  eyeball  the  venae  vorticosae  will  be 
noticed  issuing  from  the  sclerotic  coat  at  wide  intervals  from  each  other, 
and  on  approaching  the  posterior  aspect  of  the  eyeball  the  posterior  ciliary 
arteries  and  the  ciliary  nerves  will  be  seen  piercing  the  same  coat  around 
t he  entrance  of  the  optic  nerve. 

Before  beginning  the  actual  dissection  of  the  eyeball,  it  is  important 
that   the   Student    should   obtain   a  general   conception  of  the   parts  which 


564 


THE  EYEBALL 


compose  it.  This  can  best  be  done  by  selecting  two  of  the  specimens  and 
making  sections  through  them  in  two  different  planes.  One  specimen  may 
be  divided  at  the  equator  into  an  anterior  and  a  posterior  portion,  whilst 
the  other  may  be  divided  in  an  antero-posterior  direction  into  a  mesial  and 
a  lateral  half  To  obtain  satisfactory  sections  it  is  necessary  that  the  eye- 
balls should  in  the  first  instance  be  hardened  in  a  15  per  cent  solution  of 
formalin.  When  the  sections  are  made,  they  should  be  placed  under 
water  in  a  cork -lined  tray,  and  preserved  for  reference  as  the  study  of  the 
eyeball  is  proceeded  with. 

General  Structure  of  the  Eyeball. — The  eyeball  consists 
of  three  concentrically  arranged  coats  enclosing  a  cavity  in 
which  are  placed  three  refracting  media. 


Suspensory  ligament  of  lens 
Ciliary  muscle 

Canal  of  Petit  -^ 


Iris 

Posterior  chamber 
Canal  of  Schlemm 

Conjunctiva 

Ciliary  process 

Ora  serrata 
Tendon  of 
rectus  interims 

Sclerotic 
Choroid 

Retina 


Canal  of  Stilling 

Optic  nerve 

Sheath  of  dura  mater 


Macula 


Fig.  232. — Horizontal  section  through  the  Left  Eyeball. 
(Diagrammatic.) 


The  tunics  are:  (1)  an  external  fibrous  envelope  com- 
posed of  a  posterior  opaque  part,  called  the  sclerotic  coat,  and 
an  anterior  clear  transparent  portion  called  the  cornea;  (2) 
an  intermediate  vascular  envelope,  in  which  we  recognise 
three  subdivisions,  viz.,  a  hinder  part  called  the  choroid  coat,  a 
front  portion  termed  the  iris,  which  lies  behind  the  cornea, 
and  an  intermediate  ciliaiy  zone ;  (3)  the  nervous  inner  tunic 
or  retina  in  wThich  the  fibres  of  the  optic  nerve  spread  out. 

The  refracting  media  are:  (1)  behind  the  cornea  a  watery 
fluid,  called  the  aqueous  humour,  contained  in  a  space 
partially  subdivided  by  the  iris  into  the  two  chambers  of  the 
eye;  (2)  the  crystalli?ie  lens  behind   this;  and  (3)  the  vitreous 


SCLEROTIC  COAT  565 

body,    occupying    the   posterior   part    of   the   interior   of   the 
eyeball. 

Dissection. — The  superficial  surface  of  the  sclerotic  coat  and  the  cornea 
should  now  be  examined  ;  but  to  complete  the  study  of  the  external  tunic, 
a  further  dissection  is  required.  Selecting  an  eyeball  for  this  purpose,  an 
incision  should  be  made  with  a  sharp  knife  through  the  sclerotic  at  the 
equator.  This  must  be  done  carefully,  and  the  moment  that  the  sub- 
jacent black  choroid  coat  appears  the  knife  should  be  laid  aside.  The  cut 
edge  of  the  sclerotic  should  now  be  seized  with  the  forceps,  and  the 
incision  carried  completely  round  the  eyeball  with  the  scissors  along  the 
line  of  the  equator.  The  outer  fibrous  tunic  is  thus  divided  into  an 
anterior  and  a  posterior  portion.  These  must  now  be  raised  from  the 
subjacent  parts.  As  the  anterior  portion  is  turned  forwards,  some  resist- 
ance will  be  met  close  to  the  margin  of  the  cornea  from  the  attachment  of 
the  ciliary  muscle  to  the  deep  surface  of  the  sclerotic.  This  can  easily  be 
broken  through  with  the  blunt  point  of  the  closed  forceps  ;  as  soon  as  this 
is  done  the  aqueous  humour  escapes.  In  the  case  of  the  posterior  part  of 
the  sclerotic,  its  complete  separation  can  be  effected  by  dividing  the  fibres 
of  the  optic  nerve  close  to  the  point  where  they  appear  through  the 
sclerotic. 

When  the  above  dissection  is  successfully  carried  out,  the  outer  fibrous 
tunic  is  isolated  in  two  portions,  whilst  a  continuous  view  of  the  inter- 
mediate vascular  coat  is  obtained.  The  eyeball,  denuded  of  its  external 
tunic,  should  now  be  placed  in  a  shallow  vessel  filled  with  water. 

Sclerotic  Coat. — The  sclerotic  is  what  is  commonly  known 
as  the  white  of  the  eye.  It  is  a  dense,  resistant  tunic, 
opaque-white  in  colour,  which  envelops  the  posterior  five- 
sixths  of  the  globe  of  the  eye.  It  is  thickest  behind,  and 
becomes  thinner  as  it  is  traced  forwards.  Near  the  cornea, 
however,  it  again  becomes  thicker  owing  to  the  accession  of 
fibres  which  it  receives  from  the  tendons  of  the  ocular 
muscles.  Except  at  the  optic  entrance  and  close  to  the 
margin  of  the  cornea,  where  it  adheres  to  the  surface  of  the 
subjacent  ciliary  muscle,  the  deep  surface  of  the  sclerotic  is 
very  loosely  attached  to  the  choroid  coat.  Some  pigmented 
flocculent  connective  tissue  (lamina  fusca)  passes  betwreen 
the  two  coats  and  traverses  what  is  in  reality  an  extensive 
lymph  space,  termed  the  perichoroidal  space. 

The  point  at  which  the  optic  nerve  pierces  the  back  part 
of  the  sclerotic  does  not  correspond  with  the  posterior  pole 
of  the  eyeball.  The  optic  entrance,  as  it  is  termed,  is  situated 
about  3  mm.  to  the  inner  or  nasal  side  of  the  posterior  pole 
and  very  slightly  below  it.  Here  the  outer  fibrous  sheath  of 
the  optic  nerve,  which  is  derived  from  the  dura  mater,  blends 
with  the  sclerotic  coat,  whilst  the  bundles  of  nerve  fibres  are 
carried  forwards  through  a  series  of  small  apertures.  This 
perforated  portion  of  the  sclerotic  is  called  the  lamina  cribrosa. 


566 


THE  EYEBALL 


The  sclerotic  coat  is  also  pierced  by  numerous  blood  vessels  and  nerves. 
Thus  the  long  and  short  posterior  ciliary  arteries  with  the  ciliary  nerves 
perforate  the  sclerotic  around  the  optic  entrance  ;  four  or  five  vena: 
vorticosse  issue  from  the  interior  of  the  eyeball  by  piercing  the  sclerotic  a 
little  way  behind  the  equator  at  wide  intervals  from  each  other  ;  whilst 
the  anterior  ciliary  arteries  pierce  the  same  coat  near  the  corneal  margin. 

In  front  the  sclerotic  coat  is  not  only  contiguous  with,  but 
is  directly  and  structurally  continuous  with,  the  cornea.  This 
is  termed  the  corneoscleral  junction,  and  the  faint  groove  on 
the  surface  which  corresponds  with  it  receives  the  name  of 
the  scleral  sulcus.  At  this  junction  the  sclerotic  tissue  slightly 
overlaps  the  corneal  tissue,  so  that  the  line  of  union  when 


Vena  vorticosa 
Long  posterior 


Optic  entrance 
Short  ciliary 
arteries  and 
ciliary  nerves 


Fig.  233. — Diagram  of  the  posterior  aspect  of  the  Left  Eyeball.  The 
excentric  position  of  the  optic  entrance  is  somewhat  exaggerated. 
(After  Testut,  modified. ) 

seen  in  section  is  oblique.  Close  to  this  a  minute  canal  in 
the  substance  of  the  sclerotic,  termed  the  canal  of  Schlewm, 
encircles  the  margin  of  the  cornea. 

Cornea. — The  cornea  forms  the  anterior  sixth  of  the  outer 
fibrous  tunic  of  the  globe  of  the  eye.  It  is  transparent  and 
glass-like,  and  it  forms  the  window  through  which  the  rays  of 
light  gain  admittance  into  the  eyeball.  The  curvature  of  the 
cornea  is  more  accentuated  than  that  of  the  sclerotic,  and 
thus  it  constitutes  the  segment  of  a  smaller  sphere.  When 
viewed  from  behind  it  appears  circular,  but  when  looked  at 
from  the  front  it  is  seen  to  be  slightly  wider  in  the  transverse 
direction.  This  is  due  to  the  fact  that  the  sclerotic  overlaps 
it  to  a  greater  extent  above  and  below  than  it  does  at  the 
sides.  This  is  particularly  noticeable  in  the  eyeball  of  the 
ox.     The  posterior  concave  surface  of  the  cornea  forms  the 


CHOROID  COAT  567 

front  boundary  of  the  anterior  chamber  of  the  eyeball,  and  is 
separated  by  the  aqueous  humour  from  the  anterior  surface  of 
the  iris. 

The  anterior  convex  surface  of  the  cornea  is  clothed  by 
the  conjunctiva,  which  is  here  reduced  to  its  epithelial  layer. 
On  its  posterior  aspect  there  is  an  elastic  glassy  stratum, 
termed  the  elastic  membrane  of  Descemet  When  the  cornea 
is  relaxed  this  membrane  becomes  wrinkled,  and  it  can  be 
torn  away  in  shreds  from  the  proper  corneal  tissue.  When 
dealt  with  in  this  way  the  portions  removed  show  a  tendency 
to  curl  up. 

Ligamentum  Pectinatum  Iridis. — At  the  margin  of  the 
cornea  the  membrane  of  Descemet  becomes  fibrillar,  and 
some  of  its  fibres  are  continued  into  the  iris,  forming  the 
pillars  of  the  iris  or  the  ligamentum  pectinatum  iridis,  whilst 
others  are  prolonged  backwards  into  the  choroid  and  the 
sclerotic.  The  ligamentum  pectinatum  iridis  bridges  across 
the  angle  between  the  cornea  and  the  iris,  and  the  bundles 
of  fibres  into  which  the  membrane  of  Descemet  breaks  up  in 
this  region  constitute  an  annular  meshwork  or  sponge-like 
series  of  minute  spaces  termed  the  spaces  of  Fontana.  These 
communicate  with  the  anterior  chamber  of  the  eyeball,  and 
are  filled  with  lymph  or  aqueous  humour. 

Intermediate  Vascular  Tunic. — The  intermediate  or  vas- 
cular tunic  is  exposed  in  its  entire  extent  in  the  eyeball,  from 
which  the  sclerotic  coat  and  the  cornea  have  been  removed. 
As  previously  mentioned,  the  vascular  tunic  consists  of  three 
portions,  viz.,  a  choroid  coat,  a  ciliary  zone,  and  the  iris.  The 
choroid  coat  is  the  dark-coloured  portion  which  lies  behind 
the  ciliary  muscle.  The  ciliary  zo?ie  consists  of  a  superficial 
ciliary  muscle  and  the  subjacent  ciliary  processes.  The  ciliary 
muscle  presents  the  appearance  of  a  conspicuous  white  ring- 
like  band,  which  encircles  the  fore-part  of  the  eyeball  immedi- 
ately behind  the  corneo-scleral  junction.  The  ciliary  processes 
are  directly  continuous  behind,  under  the  ciliary  muscle,  with 
the  choroid  coat,  and  also  in  front  with  the  iris.  The  iris  is 
a  circular  curtain  with  a  central  aperture  which  lies  behind 
the  cornea. 

Choroid  Coat. — This  is  pierced  behind  by  the  optic  nerve, 
and  is  somewhat  thicker  behind  than  it  is  in  front.  Its 
superficial  surface  is  connected  with  the  deep  surface  of  the 
sclerotic    by   some   lax   connective   tissue    and   also  by   blood 


568 


THE   EYEBALL 


vessels  and  nerves  which  pass  from  the  one  into  the  other. 
The  deep  surface  of  the  choroid  is  moulded  upon  the  retina 
and  connected  with  a  layer  of  deeply-pigmented  cells,  which 
usually  adheres  to  the  choroid  when  this  tunic  is  removed, 
although  in  reality  it  must  be  regarded  as  a  portion  of  the 
retina. 

In  the  eyes  of  many  mammals,  but  not  in  man,  the  posterior  part  of  the 
choroid  when  viewed  from  the  front  presents  an  extensive  brightly-coloured 
area,  which  exhibits  a  metallic  lustre.  This  appearance  is  due  to  the 
presence  of  an  additional  layer  in  the  choroid  termed  the  tapetum.  In  the 
horse,  elephant,  ox,  the  tapetum  is  composed  of  fibres  (tapetum  fibrosum)  ; 
in  carnivora,  it  is  formed  of  cells  (tapetum  cellulosum).  In  the  ox,  it  is  a 
brilliant  green  colour  with  a  golden  lustre  ;  in  the  dog,  it  is  white  with  a 
bluish  border  ;  in  the  horse,  it  is  blue  with  a  silvery  lustre. 


Cornea 


Canal  of  Schlemm 

Anterior  ciliary 
artery 


Sclerotic  coat 


Vena  vorticosa 


Long  posterior 
ciliary  artery 


Anterior  ciliary 
artery 

Ciliary  muscle 


Long  posterior 
ciliary  artery 

Vena  vorticosa 


Long  posterior 
ciliary  artery 


Fig.  234. — Dissection  of  the  Eyeball  showing  the  Vascular  Tunic  and 
the  Distribution  of  the  Ciliary  Nerves  and  Vessels. 


The  chief  bulk  of  the  choroid  coat  is  composed  of  blood 
vessels.  These  are  arranged  in  two  well-marked  layers,  viz., 
a  deep,  closely-meshed  capillary  layer  called  the  tunica  chorio- 
capillaris  or  the  tunica  Ruyschiana,  and  a  more  superficial 
venous  layer  composed  of  the  vasa  vorticosa.  The  short 
posterior  ciliary  arteries  proceed  forwards  between  these 
vascular  layers. 

The  eyeball  in  which  the  outer  surface  of  the  choroid  is  exposed  should 
be  immersed  in  water  and  the  pigment  washed  out  of  it  by  means  of  a 
camel-hair  brush.  The  vasa  vorticosa  will  then  appear  as  white  curved 
lines  converging  towards  four  or  five  points,  from  which  the  larger  vencc 
vorticosce  take  origin  (Fig.  234). 


CILIARY  PROCESSES 


569 


Ciliary  Muscle. — This  is  composed  of  involuntary  muscular 
tissue,  but  the  arrangement  of  its  fibres  can  only  be  seen 
when  thin  sections  of  the  eyeball  are  examined  under  the 
microscope.  The  fibres  are  then  observed  to  be  disposed  in 
two  groups,  viz.,  a  radiating  and  a  circular. 

The  radiating  fibres  arise  from  the  deep  aspect  of  the 
sclerotic  coat  close  to  the  margin  of  the  cornea.  From  this 
they  radiate  backwards  in  a  meridional  direction,  and  gain 
insertion  into  the  choroid  coat  in  the  region  of  the  ciliary 
processes. 

The  circular  fibres  consist  of  two  or  three  bundles  placed 
upon  the  deep  aspect  of  the  radiating  portion  of  the  muscle. 
They  form  a  muscular  ring  around  the  circumference  of  the 
iris. 


-%  Ciliary  process 


FlG.    235.— The  Ciliary  Processes  of  the  Human   Eyeball, 
viewed  from  behind.      (From  Merkel. ) 

Dissection. — To  obtain  a  view  of  the  ciliary  processes,  a  coronal  section 
should  be  made  with  the  scissors  through  an  eyeball  a  short  distance  in 
front  of  the  equator.  The  portion  of  the  vitreous  body  which  occupies  the 
anterior  segment  of  the  eyeball  should  be  carefully  removed.  When  this 
is  done,  the  deep  aspect  of  the  ciliary  processes  will  be  seen  as  they  radiate 
backwards  from  the  circumference  of  the  crystalline  lens.  By  washing  out 
the  pigment  from  this  part  of  the  vascular  tunic,  the  arrangement  of  the 
processes  will  be  more  fully  displayed. 

A  second  dissection  may  be  made  in  another  eyeball  with  the  object  of 
exposing  the  ciliary  processes  from  the  front.  In  this  case  remove  the 
cornea  with  the  scissors  by  cutting  round  the  corneo-scleral  junction.  The 
iris  is  now  brought  conspicuously  into  view,  and  may,  with  advantage,  be 
studied  at  this  stage.  Several  cuts  in  the  meridional  direction,  and  at 
equal  intervals  from  each  other,  should  in  the  next  place  be  made  through 
the  anterior  part  of  the  sclerotic  coat.  The  strips  of  sclerotic  should  then 
be  separated  from  the  ciliary  muscle,  and  pinned  backwards  in  a  cork- 
lined  tray  filled  with  water.  The  last  step  in  the  dissection  consists  in  the 
removal  of  the  iris. 

Ciliary  Processes.— When  the  choroid  coat  is  traced 
forwards  under  the  ciliary  muscle,  it  is  seen  to  form  a  series 
of  elongated  prominent  thickenings,  which  radiate  backwards 
from  the  margin   of  the   crystalline   lens   like   the   folds   of  a 


57o  THE  EYEBALL 

goffered  frill.  These  thickenings  are  the  ciliary  processes. 
They  vary  slightly  in  their  degree  of  prominence,  and  also  in 
length,  but  they  are  very  constant  in  number.  In  the  human 
eye  seventy  ciliary  processes,  as  a  rule,  may  be  counted.  As 
each  process  proceeds  forwards,  it  becomes  gradually  more 
and  more  prominent,  until  ultimately  it  ends  in  a  thickened 
projection,  which  occupies  the  space  between  the  margin  of 
the  iris  and  the  circumferential  part  of  the  anterior  surface  of 
the  crystalline  lens.  In  this  position  the  ciliary  processes 
bound  peripherally  the  posterior  chamber  of  the  eyeball 
(Fig.  236). 

The  ciliary  processes  rest  upon  the  subjacent  zonule  of 
Zinn,  i.e.,  the  membrane  which  covers  the  fore-part  of  the 
vitreous  body.  This  membrane  is  adapted  in  the  most 
intimate  manner  to  the  ciliary  processes.  It  is  folded  or 
wrinkled  in  such  a  way  that  the  folds  occupy  the  sulci  or 
valleys  between  the  processes. 

Iris. — The  iris  lies  in  front  of  the  crystalline  lens,  and  it 
is  separated  from  the  cornea  by  the  anterior  chamber  filled 
with  aqueous  humour.  By  its  circumference  it  is  continuous 
with  the  ciliary  body,  and  it  is  at  the  same  time  connected 
by  the  ligamentum  pectinatum  iridis  with  the  margin  of  the 
cornea. 

The  iris  is  circular  in  form,  and  is  perforated  in  the  centre 
by  a  round  opening  which  is  termed  the  pupil.  Its  anterior 
surface  is  faintly  striated  in  a  radial  direction.  It  is  coloured 
differently  in  different  individuals.  Its  posterior  surface  is 
deeply  pigmented.  The  pupil  presents  a  very  nearly  circular 
outline,1  and  during  life  it  constantly  varies  in  its  dimensions 
so  as  to  control  the  amount  of  light  which  is  admitted  into 
the  interior  of  the  eyeball.  These  changes  in  the  size  of  the 
pupil  are  produced  by  the  contractile  properties  of  two 
groups  of  involuntary  muscular  fibres  which  are  present  in 
the  substance  of  the  iris.  One  group  is  composed  of  muscular 
fibres  arranged  circularly  around  the  pupil  in  the  form  of  a 
sphincter  \  the  second  group  consists  of  fibres  which  have  a 
radial  direction,  and  pass  from  the  sphincter  towards  the 
circumference    of   the    iris,    so    as    to    constitute   a   dilatator 


1  It  may  be  as  well  to  mention  here  that  the  pupil  in  the  ox  and  the 
sheep  is  greatly  elongated  in  the  transverse  direction.  In  the  pig,  how- 
ever, it  is  approximately  circular. 


VEN^E  VORTICOSE  571 

muscle.  By  certain  anatomists  these  radial  fibres  are  considered 
to  be  elastic  and  not  muscular. 

Ciliary  Nerves. — The  ciliary  nerves  which  arise  from  the 
lenticular  ganglion  and  the  nasal  nerve,  after  piercing  the 
sclerotic  at  the  back  of  the  eyeball  around  the  optic  entrance, 
extend  forwards  between  this  coat  and  the  choroid  in  the 
perichoroidal  lymph  space.  They  will  be  seen  in  the 
specimen  in  which  the  sclerotic  has  been  turned  backwards 
in  separate  flaps  in  the  form  of  delicate  white  filaments 
(Fig.  234).  In  the  posterior  part  of  the  eyeball  they  occupy 
grooves  on  the  deep  surface  of  the  sclerotic,  and  can  only  be 
separated  from  it  with  difficulty.  Reaching  the  ciliary  zone 
the  ciliary  nerves  break  into  branches,  which  join  in  a  plexi- 
form  manner  and  send  twigs  to  the  ciliary  muscle,  the  iris, 
and  the  cornea. 

Ciliary  Arteries.  —  Of  these  we  recognise  three  groups, 
viz.: — (1)  the  short  posterior  ciliary  arteries;  (2)  the  long 
posterior  ciliary  arteries;  and  (3)  the  anterior  ciliary 
arteries. 

The  short  posterior  ciliary  arteries,  branches  of  the 
ophthalmic,  pierce  the  sclerotic  around  the  optic  entrance, 
and  are  distributed  in  the  choroid  coat  between  the  vasa 
vorticosa  and  the  membrana  chorio-capillaris. 

The  long  posterior  ciliary  arteries,  also  branches  of  the 
ophthalmic,  are  only  two  in  number.  They  perforate  the 
sclerotic  on  either  side  of  the  optic  nerve  (Fig.  234),  a  short 
distance  beyond  the  short  ciliary  arteries,  and  are  then 
carried  forwards  between  the  sclerotic  coat  and  the  choroid. 
When  they  gain  the  ciliary  zone  each  artery  divides  into  an 
ascending  and  a  descending  branch,  and  these,  with  the 
anterior  ciliary  arteries,  form  an  arterial  ring  termed  the 
circulus  iridis  major.  From  this  branches  are  given  to  the 
ciliary  muscle,  the  ciliary  processes,  and  the  iris. 

The  circulus  iridis  minor  is  the  name  applied  to  a  second  arterial  ring 
in  the  iris  at  the  outer  border  of  the  sphincter  pupillse. 

The  anterior  ciliary  arteries  are  very  small  twigs,  which 
arise  from  the  branches  of  supply  to  the  recti  muscles. 
They  pierce  the  sclerotic  close  to  the  margin  of  the  cornea, 
take  part  in  the  formation  of  the  circulus  iridis  major,  and 
send  twigs  to  the  ciliary  processes. 

Venae    Vorticosae.  —  From     each     venous    vortex    in     the 


572  THE  EYEBALL 

choroid  a  large  vein  arises,  which  makes  its  exit  from  the 
eyeball  by  piercing  the  sclerotic  obliquely  a  short  distance 
behind  the  equator.      They  are  four  or  five  in  number. 

Dissection.- — The  vitreous  body  and  retina  in  the  hinder  part  of  the 
eyeball,  which  was  cut  into  two  for  the  purpose  of  exposing  the  ciliary 
processes  from  behind,  should  now  be  dislodged.  By  raising  the  choroid 
coat  from  the  deep  surface  of  the  sclerotic,  under  a  flow  of  water  from 
the  tap,  the  vence  vorticosas  entering  the  deep  surface  of  the  sclerotic 
will  be  brought  into  view.  When  these  are  divided,  and  the  separation 
of  the  two  coats  is  carried  back  towards  the  optic  entrance,  the  posterior 
short  ciliary  arteries,  as  they  emerge  from  the  sclerotic  and  enter  the  back 
part  of  the  choroid,  will  be  seen. 

In  the  eyeball  from  which  the  sclerotic  and  cornea  have  been  removed, 
the  iris,  ciliary  processes,  and  the  choroid  should  be  carefully  stripped  off 
piecemeal  under  water.     This  will  expose  the  retina. 

Retina.  —  The  retina  is  composed  of  two  strata — viz.,  a 
thin  pigmentary  layer,  which  adheres  to  the  deep  surface  of 
the  choroid  coat,  and  has  been  removed  with  it,  and  a 
delicate  ?iervous  layer,  which  is  moulded  on  the  surface  of 
the  vitreous  body,  but  presents  no  attachment  to  it  except  at 
the  optic  entrance.  The  retina  extends  forwards  beyond 
the  equator  of  the  eyeball,  and  a  short  distance  from  the 
ciliary  zone  it  appears  to  end  in  a  well-defined  wavy  or 
festooned  border  termed  the  ora  serrata.  This  appearance, 
however,  is  somewhat  deceptive.  The  nerve  elements,  it 
is  true,  come  to  an  end  along  this  line,  but  a  lamina  in 
continuity  with  the  retina  is  in  reality  prolonged  forwards 
as  far  as  the  margin  of  the  pupil.  The  part  in  relation  to 
the  ciliary  processes  is  exceedingly  thin,  and  cannot  be 
detected  by  the  naked  eye.  It  is  termed  the  pars  ciliaris 
refaicE.  The  portion  on  the  deep  surface  of  the  iris  forms  its 
posterior  uveal  pigmentary  layer  (pars  iridica  retinae). 

During  life  the  retina  proper  is  transparent,  but  after  death 
it  soon  assumes  a  dull  greyish  tint  and  becomes  opaque. 
Posteriorly  it  is  tied  down  at  the  optic  entrance.  When 
viewed  from  the  front  this  appears  as  a  conspicuous  circular 
disc  termed  the  poms  opticus  or  optic  disc.  From  this  spot 
the  optic  nerve  fibres  radiate  out  so  as  to  form  the  deep  or 
anterior  layer  of  the  retina.  The  optic  disc,  in  correspond- 
ence with  the  entrance  of  the  optic  nerve,  lies  to  the  inner 
or  nasal  side  of  the  antero -posterior  axis  of  the  eyeball. 
Exactly  in  the  centre  of  the  human  retina,  and  therefore  in 
the  axis  of  the  globe  of  the  eye,  there  is  a  small   yellowish 


VITREOUS  BODY  573 

spot  termed  the  macula  lutea?-  It  is  somewhat  oval  in 
outline,  and  in  its  centre  it  is  depressed,  thereby  forming 
what  is  called  the  fovea  centralis. 

Retinal  Arteries  and  Veins.- — In  a  fresh  eyeball  the 
arteria  retina  centralis  will  be  seen  entering  the  retina  at 
the  optic  disc.  It  immediately  divides  into  an  ascending 
and  a  descending  branch,  and  each  of  these  breaks 
up  into  a  large  outer  or  temporal  division,  and  a  smaller 
inner  or  nasal  division.  These  ramify  in  the  retina  as  far  as 
the  ora  serrata  ;  but  the  resultant  branches  do  not  anastomose 
with  each  other  nor  with  any  of  the  other  vessels  in  the 
eyeball. 

The  retinal  veins  converge  upon  the  optic  disc,  and 
disappear  into  the  substance  of  the  optic  nerve  in  the  form 
of  two  small  trunks  which  soon  unite. 

The  retinal  vessels,  the  optic  disc,  and  the  macula  can  all  be  examined 
in  the  living  eye  by  means  of  the  ophthalmoscope.  The  red  reflex  obtained 
from  the  fundus  of  the  eyeball  is  produced  by  the  blood  in  the  membrana 
chorio-capillaris. 

Dissection. — For  the  study  of  the  vitreous  body  and  the  crystalline  lens, 
which  together  maybe  termed  the  "eye-kernel,"  it  is  better  to  take  an 
eyeball  which  is  not  perfectly  fresh  (Anderson  Stuart).  The  eyeball 
selected  for  this  purpose  should  be  allowed  to  stand  untouched  from  one 
to  three  days  according  to  the  season.  The  coats  of  the  eye  should  then 
be  divided  round  the  equator,  and  on  gently  separating  the  cut  edges,  and 
turning  the  coats  forwards  and  backwards,  the  "  eye-kernel"  will  slip  out. 
It  should  be  allowed  to  drop  into  a  vessel  filled  with  clean  water.  The 
examination  of  the  parts  forming  the  eye-kernel  will  be  greatly  facilitated 
by  placing  it  en  masse  in  strong  picro-carmine  solution  for  a  few  minutes. 
When  removed  from  the  staining  fluid,  it  should  be  well  washed  in  water. 
In  this  way  the  hyaloid  membrane  enclosing  the  vitreous  body,  the  capsule 
of  the  lens,  and  the  zonula  of  Zinn,  are  stained  red,  and  their  connexions 
become  very  apparent  (Anderson  Stuart). 

Vitreous  Body. — This  is  a  soft,  yielding,  perfectly  trans- 
parent jelly-like  body,  which  occupies  the  posterior  four-fifths 
of  the  interior  of  the  eyeball.  The  retina  is  spread  over  its 
surface  as  far  forwards  as  the  ora  serrata,  but  is  in  no  wax- 
attached  to  it,  except  at  the  optic  disc.  In  front  of  the  ora 
serrata,  the  ciliary  processes  are  applied  to  the  vitreous  body 
and  indent  its  surface.  Anteriorly,  the  vitreous  body  is 
hollowed  out,  and  presents  a  deep  concavity,  the  fossa  patel- 
lars, for  the  reception  of  the  posterior  convex  surface  of  the 
crystalline  lens. 


I  here  is  no  macula  Intra  in  the  eyeball  of  the  ox  or  sin-. -p. 


574 


THE  EYEBALL 


The  substance  of  the  vitreous  body  is  enclosed  within  a 
delicate  transparent  membrane,  which  completely  envelops 
it,  and  receives  the  name  of  the  hyaloid  membrane.  Extend- 
ing forwards  through  the  midst  of  the  vitreous  mass  from  the 
region  of  the  optic  disc  to  the  back  of  the  crystalline  lens  is 
a  minute  canal,  lined  by  a  tube-like  prolongation  of  the 
hyaloid  membrane,  and  containing  a  watery  fluid.  This  is 
termed  the  hyaloid  canal,  or  the  canal  of  Stilling,  and  it  re- 
presents the  path  which  was  taken  by  a  branch  of  the  arteria 
retinae  centralis,  which  in  the  foetus  extends  forwards  for  the 
supply  of  the  capsule  of  the  lens,  but  afterwards  disappears. 


Retina 


Sclerotic 


suprachoroid  space 

Ciliary  muscle  (radiating  fibres) 

Ciliary  muscle  (circular  fibres) 
Canal  of  Schlemm 

Spaces  of  Fontana 
-   Ciliary  process 
Canal  of  Petit 

Suspensory  ligament 

Iris 

Cornea 


Fig.  236. — Diagrammatic  representation  of  the  Ciliary  Region, 
as  seen  in  vertical  section. 

The  canal  of  Stilling,  as  a  rule,  cannot  be  seen  in  an  ordinary  dissection 
of.  the  eyeball ;  but  if  the  eye-kernel  be  shaken  up  in  the  picro-carmine 
solution  as  recommended  by  Anderson  Stuart,  it  may  sometimes  be  rendered 
evident  through  the  staining  fluid  entering  it. 

Zonula  of  Zinn  and  the  Suspensory  Ligament  of  the  Lens. 

— In  the  ciliary  region  the  hyaloid  membrane  of  the  vitreous 
body  becomes  thickened  and  strengthened,  and  forms  what 
is  termed  the  zonula  of  Zinn.  As  this  approaches  the  margin 
of  the  crystalline  lens,  it  splits  into  two  parts,  viz.,  an  exceed- 
ingly delicate  deep  lamina,  which  lines  the  fossa  patellaris, 
and  a  more  superficial  stronger  part,  which  becomes  attached 
to  the  capsule  of  the  crystalline  lens. 

The  zonula  of  Zinn  lies  subjacent  to  the  ciliary  processes, 
and  is  radially  plaited   or   wrinkled  in    correspondence  with 


CRYSTALLINE  LENS  575 

these.  Thus  the  elevations  or  wrinkles  of  the  zonula  extend 
into  the  intervals  between  the  ciliary  processes,  whilst  the 
ciliary  processes  in  their  turn  lie  in  the  depressions  between 
the  wrinkles  of  the  zonula.  When  the  eye  is  fresh,  these 
opposing  parts  are  closely  adherent. 

The  zonula  of  Zinn  is  strengthened  by  radially  directed 
meridional  elastic  fibres,  and  after  the  delicate  membrane 
which  lines  the  fossa  patellaris  is  given  off  from  its  deep 
surface,  it  extends  forwards  as  a  distinct  layer,  and  is  attached 
to  the  anterior  surface  of  the  capsule  of  the  lens  a  short 
distance  beyond  the  margin  of  that  body.  In  this  manner 
the  suspensory  ligament  of  the  lens  is  formed.  But  this  is  not 
the  only  attachment  of  the  suspensory  ligament.  Some 
scattered  fibres  are  attached  to  the  circumference  or  equator 
of  the  lens  (equatorial  fibres),  whilst  others  are  fixed  to  its 
posterior  surface  close  to  its  margin  (post-equatorial  fibres). 

In  this  way  the  crystalline  lens  is  firmly  held  in  its  place 
in  the  fossa  patellaris.  Further,  the  degree  of  tension  of  its 
suspensory  ligament  is  influenced  by  the  radiating  fibres  of 
the  ciliary  muscle,  which  by  their  contraction  pull  upon  the 
ciliary  processes,  and  produce  relaxation  of  the  zonula  of  Zinn. 

Canal  of  Petit. — This  is  a  circular  lymph  space,  which 
surrounds  the  circumference  of  the  lens.  It  is  bounded  in 
front  by  the  suspensory  ligament,  and  behind  by  the  hyaloid 
membrane,  enclosing  the  vitreous  body.  It  is  filled  with  a 
watery  fluid. 

By  introducing  the  point  of  a  fine  blow-pipe  into  the  canal  of  Petit 
through  the  suspensory  ligament,  it  can  be  partially,  or,  perhaps,  com- 
pletely, inflated  with  air.      It  then  presents  a  sacculated  appearance. 

Dissection. — The  crystalline  lens  may  he  removed  by  snipping  through 
the  suspensory  ligament  with  scissors. 

Crystalline  Lens. — The  crystalline  lens  is  a  biconvex, 
solid,  and  transparent  structure,  which  lies  behind  the  iris, 
and  in  front  of  the  vitreous  body.  It  is  enclosed  within  a 
glassy,  elastic  capsule,  to  which  the  different  parts  of  the 
suspensory  ligament  are  firmly  cemented,  and  it  presents  for 
study  an  anterior  surface,  a  posterior  surface,  and  a  circum- 
ference  or  equator. 

The  anterior  surface  is  not  so  highly  curved  as  the  posterior 
surface.  Its  central  part  which  corresponds  with  the  pupillary 
aperture  of  the  iris   looks  forward    into   the   anterior   chamber 


576  THE  EYEBALL 

of  the  eye.  Around  this  part  the  margin  of  the  pupillary 
orifice  of  the  iris  is  in  contact  with  the  lens,  whilst  nearer  the 
equator  the  anterior  surface  of  the  lens  is  separated  from  the 
iris  by  the  fluid  in  the  posterior  chamber  of  the  eyeball.  The 
posterior  surface  of  the  lens  presents  a  higher  degree  of  curva- 
ture than  the  anterior  surface,  and  is  received  into  the  fossa 
patellaris  of  the  vitreous  body.  The  equator  or  circumference 
is  rounded.  It  forms  one  of  the  boundaries  of  the  canal  of 
Petit,  and  the  manner  in  which  the  suspensory  ligament  is 
attached  to  the  capsule  in  this  vicinity  has  already  been 
described. 

Faint  radiating  lines  may  be  seen  on  both  surfaces  of  the 
lens.  These  give  a  clue  to  the  structure  of  the  lens.  They 
indicate  the  planes  along  which  the  extremities  of  the  lens- 
fibres  come  into  apposition  with  each  other. 

The  capsule  of  the  lens  is  a  resistant  glassy  membrane, 
which  is  considerably  thicker  in  front  than  behind. 

The  anterior  wall  of  the  capsule  may  now  be  divided  with  a  sharp  knife. 
A  little  pressure  will  cause  the  body  of  the  lens  to  escape  through  the 
opening.  The  stained  capsule,  whilst  floating  in  water,  can  be  very  ad- 
vantageously studied. 

If  the  lens  body  be  compressed  between  the  finger  and  thumb,  it  will 
be  observed  that  the  outer  portion  or  cortical  part  is  soft,  whilst  the  central 
part  or  nucleus  is  distinctly  firmer.  When  the  lens  is  hardened  in  alcohol 
it  can  easily  be  proved  that  it  is  composed  of  numerous  concentrically 
arranged  laminae. 

Chambers  of  the  Eyeball. — The  a?iterior  chamber  of  the 
eyeball  is  the  space  between  the  cornea  in  front,  and  the  iris 
and  central  part  of  the  lens  behind.  At  the  irido-corneal 
angle,  it  is  bounded  by  the  ligamentum  pectinatum,  and 
here  the  aqueous  humour  which  fills  this  chamber  finds  access 
to  the  spaces  of  Fontana. 

The  posterior  chamber  is  a  circular  space  or  interval  which 
is  bounded  in  front  by  the  posterior  surface  of  the  iris,  and 
behind  by  the  circumferential  part  of  the  anterior  face  of  the 
lens.  Externally,  this  space  is  closed  by  the  thick  anterior 
projecting  ends  of  the  ciliary  processes.  It  is  also  filled  with 
aqueous  humour. 


INDEX 


VOL.   II — 37 


577 


INDEX. 


Acustic  tubercle,  542 

Agger  nasi,  395 

Ake  of  cerebellum,  535,  536 

thyroid  cartilage,  425 
Alveus,  495,  499 

Ampullce  of  semicircular  canals,  560 
Amygdala  of  cerebellum,  538 
Amygdaloid  nucleus,  493,  514 

tubercle,  493 
Annulus  fibrosus,  102 

ovalis,  55 
Ansa  hypoglossi,  203,  211,  229,  232 

subclavia,  321 

Vieussenii,  321 
Antihelix,  269 
Antitragus,  270 
Antrum  of  Highmore,  396 

mastoid,  549 
Aorta,  63,  67 

arch,  67,  70 

ascending,  67 

descending  thoracic,  67,  85 
Aortic  groove,  29 

cusp,  64 

orifice,  63,  64,  67,  78 

sinus,  68 

valve,  63,  64,  74 

vestibule,  64 
Apex  cornu,  174 
Apical  gland,  436 
Aponeurosis,  buccal,  303,  364 

epicranial,  106 

of  palate,  380 

pharyngeal,  371 
rtebral,  140 
Appendices,  auricular,  45,  46,  61 
Aqueduct  of  Kallopius,  404,  552 

of  Sylvius,  461,  506,  508,  510 

of  vestibule,  559 
Aqueous  humour,  564 


Arachnoid,  114,  159,  162,  441 
Arbor  vitae  cerebelli,  539 
Arcuate  fibres,  528,  531,  533 
Arcus  parieto-occipitalis,  467 

tarseus,  276,  339 
Area  postrema,  543 
Arnold,  nerve  of,  262,  315 
Artery  or  Arteries,  angular,  269 

alveolar,  285,  286 

auditory,  447 

auricular,  deep,  285 

posterior,  1 11,  204,  205,  239 
of  superficial  temporal,  251 

basal,  of  brain,  445,  451,  452 

basilar,  447 

bronchial,  31,  32,  86 

buccal,  286 

bulbar,  447 

calcarine,  448,  449 

carotid,   common,   71,    201,   202, 
216,  230 
external,    201,    202,    204,   205, 

233>  251 
internal,    119,    130,    201,    202, 
306,  307,  323,  328,  382,  444, 

449 
central,      of     anterior     cerebral, 

451 

of  brain,  445,  449,  451,  452 

middle  cerebral,  452 
posterior  cerebral,  44S 
retina,  340,  573 
cerebellar,  anterior  inferior,  447 
rior  inferior,  446 
superior,  147 

bral,  anterior,  329,  449,  450 
middle,  329,  449,  452 

posterior,  447,  453 

rvical,  ascending.   222 
deep,    I48,  223 

579 


58o 


INDEX 


Artery  or  Arteries,  cervical,  super- 
ficial, 138 
choroidal,  449 

ciliary,  anterior,  340,  566,  571 
long,  340,  566,  571 
short,  340,  566,  568,  571 
comes  nervi  phrenici,  9,  25,  34 
communicating,      anterior,     450. 

453 
posterior,  329,  449,  453 

coronary,  of  facial,  268 

of  heart,  49>.7°>  75 
cortical,  of  brain,  445,  451,  452 
of  corpus  callosum,  451 
of  cranial  cavity,  129 
crico-thyroid,  207,  236 
dental,  anterior,  386 

inferior,  285,  295 

posterior  superior,  285,  286,  404 
dorsalis  linguae,  305 
epigastric,  superior,  9 
ethmoidal,  341,  391,  400 
facial,  201,  202,  204,  237,  266 

transverse,  251,  266,  280 
frontal,  of  cerebral,  451,  452 

of  ophthalmic,  1 1 1 ,  341 
Gasserian,  329 
hyoid,  202 
incisor,  295 
infra-hyoid,  235 
infra-orbital,  386,  404 
innominate,  70,  208 
intercostal,  6,  87,  94,  151 

aortic,  6,  7 

anterior,  6,  7,  9,  10 

superior,  6,  7,  95,  223 
labial,  inferior,  268 
lachrymal,  276,  339 
laryngeal,  inferior,  222,  416,  424 

superior,  202,  236,  424 
lateral  sacral,  153 
lingual,  201,   202,  236,  299,  304 
lumbar,  151 
mammary,  9 

internal,  7,  8,  223 
masseteric,  235,  286 
mastoid,  of  occipital,  146 

of  posterior  auricular,  1 1 1 
maxillary,  internal,  238,  251,  282, 

284,  401,  403 
mediastinal,  9,  25,  8j 
meningeal,    anterior,     130,    131, 

341 
of  ascending  pharyngeal,  131 
of  occipital,  131 
of  vertebral,  131,  445 


Artery     or      Arteries,     meningeal, 
middle,    114,    130,   285,  290, 
323,  330 
small,  130,  131,  285,  290,  323, 

327,  33° 
mental,  295 
musculo-phrenic,  9 
.     mylo-hyoid,  204,  286 
nasal,  dorsal,  341 
nasal,  lateral,  269 
naso-palatine,  391,  400 
neural,  158,  170 
occipital,    112,     142,     145,     191, 

201,  202,  238 
oesophageal,  87,  222 
ophthalmic,  329,  330,  336. 339, 449 
orbital,  of  cerebral,  451,  452 

of  superficial  temporal,  252 
palatine,     ascending,     204,    306, 
308,  380 

of  ascending  pharyngeal,   310, 
380 

descending,  380,  400,  404 

inferior,  237,  309 

posterior,  404 
palpebral,  276,  339,  341 
paracentral,  451 
parietal,  of  cerebral,  452 
parieto-occipital,  448,  449 
parieto-temporal,  452 
parotid,  235,  251 
perforating,  of  internal  mammary, 

4 .  9 

pericardial,  87 

petrosal,  329 

pharyngeal,   ascending,  201,  202, 

239>  3°6,  309 

pituitary,  329 

posterior  scapular,  138,  193 

post-central,  158 

precuneal,  452 

prelaminar,  158 

prevertebral,  of  ascending  pharyn- 
geal, 309 

princeps  cervicis,  146,  148 

profunda  cervicis,  148,  223 

pterygoid,  235,  286 

pterygo-palatine,  404 

pulmonary,  31,  32,  59,  66,  90 

ranine,  304,  305,  438 

septal,  268,  391 

spheno-palatine,  400,  404 

spinal,  94,    151,    158,    170,   222, 

353>  445>  440 
sterno-mastoid,  of  occipital,  202 

239 


INDEX 


58i 


Artery  or  Arteries,  sterno-mastoid,  of 
superior  thyroid,  202, 232,  236 
stylo-mastoid,  239 
subclavian,  72,  192,  217 
branches,  220 
surgical  anatomy,  193 
subcostal,  87,  95 
sublingual,  305 
submaxillary,  204,  238 
submental,  204,  238 
supra-hyoid,  237,  305 
supra-orbital,  ill,  339,  341 
supra-scapular,  139,  192,  193,  223 
temporal,  of  cerebral,  449,  452 
deep,  286 
middle,  252,  280 
superficial,  III,  240,  251 
thymic,  9,  25,  39 
thyroid  axis,  216,  221 
inferior,  221,  241,  232 
superior,   200,    201,    202,    235, 
241 
thyroidea  ima,  71,  208,  241 
tonsillitic,  204,  238,  306,  309,  381 
tracheal,  222 
transversalis  colli,  138,  191,  192, 

193.  223 
transverse,  of  basilar,  447 
tympanic,  285,  290 
vertebral,    130,    157,     216,    221, 

348,  352,  444,  445 
vidian,  404 
Articulations.     See  Joints 
Aryteno  -  epiglottidean    folds,    376, 

411 
Arytenoid  cartilages,  424,  429 
Atrium  meatus  nasi,  394 

of  heart,  46 
Auditory  apparatus,  547 
meatus,  external,  547 

internal,  404 
ossicles,  547,  555,  562 
Auricle,  269 

Auricles  of  heart,  43,  45,  52,  61 
Auricular  appendices,  45,  46,  61 

cartilage,  270 
Auriculo-ventricular   apertures,    44, 
54,  56,  57,  61,  63,  67,  76 
bundle,  76 
groove,  44,  66 
rings,  77 

Back,  132 

blood  vessels,   150 
nerves,  134,  149 
surface  anatomy,   133 


Basal  ganglia,  514 
Basilar  sinus,  126,  129 
Bicuspid  teeth,  365 

valve,  63 
Biventral  lobule,  538 
Brachia  of  corpora   quadrigemina, 

5°8,  509 
Brachial  plexus,  191,  195 
Brain,  112,  439 

basal  ganglia,  514 

base,  439,  454 

blood-vessels,  117,  441,  444 

cerebellum,  439,  460,  533,  544 

cerebral  hemispheres,  461 

cerebrum,  461 

corpus  callosum,  461,  483,  488 

fornix,  498 

fourth  ventricle,  460,  541 

general  appearance,  439 

general     connexion     of     several 
parts,  460 

lateral  ventricles,  461,  487 

medulla  oblongata,  439,  460,  521 

meninges,  114,  441 

mesencephalon,  461,  507 

optic  thalami,  461,  502,  520 

origin  of  nerves,  456 

parts   in  posterior  cranial    fossa, 
520 

pons  Varolii,  439,  460,  533,  544 

preservation  of,  121 

removal  from  cranium,  112,  119 

septum  lucidum,  497 

third  ventricle,  461,  502 

velum  interpositum,  444,  499 
Bronchi,  31,  32,  79,  90 

eparterial,  33,  80,  90 

hyparterial,  33,  80,  90 
Buccal  aponeurosis,  363,  364 

glands,  363 

plexus,  292 
Bucco-pharyngeal  fascia,  368 
Bulb  of"  brain,  439 

of  jugular  vein,  310 

of  lateral  ventricle,  493 

olfactory,  441,  480 
Bulla  ethmoidals,  396 
Bundle,  auriculo-ventricular,  76 

of  Vicq  d'Azyr,  499,  520 
Burdach,  column  of,  177 
Bursa,  pharyngeal,  374 

Calamus  scriptorius,  542 

Calcar  avis,  493 

'  lalcarine  fissure,  476 

Calloso-marginal  fissure,  465,  468 


5»2 


INDEX 


Canal,  carotid,  382 

central,  of  cord,  173,  176 
of  medulla,  522,  531 
of  modiolus,  561 

of  Huguier,  408 

hyaloid,  574 

infra-orbital,  383 

lachrymal,  276,  277 

mandibular.  295 

of  Petit,  575 

of  Schlemm,  566 

semicircular,  559,  560,  562 

spinal.  157 

spiral,  of  modiolus,  561 

of  Stilling,  574 
Canalis  reuniens,  562 
Canine  teeth,  365 
Canthi,  244 
Capsule,  external,  520 

internal,  502,  519 

of  lens,  576 

of  Tenon,  331,  335,  345 
Caput  cornu,  174 
Cardiac  notch,  30 

plexus,  deep,  72,  jt, 
superficial,  34,  72 

revolution,  65 
Carotid  body,  201,  202,  233 

canal,  382 

plexus,  320,  383 

sheath,  186,  202 

triangle,  199,  201 
Cartilage,  arytenoid,  424,  429 

cricoid,  178,  424,  427 

cuneiform,  417,  424,  430 

of  epiglottis,  424 

nasal,  278 

of  pinna,  270 

of  Santorini,  416,  424,  429 

septal,  389 

thyroid,  424,  425 
Cartilagines  corniculatce,  429 

sesamoidea  of  nose,  279 
Cartilago  triticea,  415 
Caruncula  lachrymalis,  245 
Cauda  equina,  162,  167 
Caudate  nucleus,  491,  493,  497.  514, 

515 
Cavernous  plexus,  323,  329,  383 

sinus,  126,  128,  323 
Cavity  of  thorax,  1,  10 
Cavum  Meckelii,  326 
Central  canal  of  cord,  173,  176 
of  medulla,  522,  531 
of  modiolus,  561 
grey  matter  of  aqueduct,  510 


Central  lobe,  465 

lobule,  535,  536 
Centre,  lower  visual,  509 

medullary,  463 
Centrum  ovale,  483 
Cerebellar   tract,   direct,    177.    525. 

528 
Cerebello-olivary  tract,  528 
Cerebellum,  439,  460,  520,  533 
arbor  vitse,  539 
corpus  dentatum,  544 

trapezoides,  539 
fissures,  535 
hemispheres,  534 
lobes,  535,  538 
lobules,  535,  537,  538,  539 
monticulus,  534 
notches,  534 
peduncles,  540,  545 
inferior,  460,  528,  540 
middle,  461,  534,  540 
superior,    461,    513,    535,    540, 

545,  546 
vallecula,  534 
vermis,  534,  535,  538 
Cerebral  cortex,  463 
hemispheres,  439,  461 

basal  ganglia,  514 

borders,  462 

centrum  ovale,  483 

corona  radiata,  520 

cortex,  463 

fissures,  462,  463,  465,  476,  496 

general  structure,  463 

grey  matter,  463 

gyri,  463,  469,  473,  474 

internal  capsule,  502,  519 

island  of  Reil,  465,  480,  493 

lobes,  465,  469,  472,  475,  477, 
480 

medullary  centre,  463 

orbital  area,  461 

poles,  462 

sulci,  463,  469,  473,  477,  478, 
480 

tentorial  area,  461 

ventricles,  460,  461,  487,  497 
Cerebrum,  461 

anterior  commissure,  505 
corpus  callosum,  461,  482,  488 
crura,  454,  461,  508,  509 
fornix,  497,  498 
grey  commissure,  504,  505 
hemispheres,  439,  461 
lateral  ventricles,  461,  487 
longitudinal  fissure,  461,  462 


INDEX 


Cerebrum,  optic  thalami,  461,  492. 
502,  520 
posterior  commissure,  505 

Cerebrum,  septum  lucidum,  497 
third  ventricle,  461,  505 
transverse  fissure,  496,  501 
velum     interpositum,     444.    491. 

501 
Ceruminous  glands,  548 
Cervical  fascia,  182,  188,  208 
ganglion,  inferior,  216,  321 
middle,  216,  321 
superior,  319 
pleura,  16,  216,  226 
plexus,  226,  306,  322 

communicating  branches,  229 
muscular  branches,  228 
superficial  branches,  181,   191, 
228 
sympathetic,  201,  203,  306.  383 
Cervix  cornu,  174 
Chambers  of  eyeball,  564,  576 
Cheeks,  363 
Chest.      See  Thorax 
Chiasma,  optic,  454 
Choanre,  373,  391 
Chords  tendinerc,  56,  63,  64 

YVillisii,  119 
Choroid  coat,  564,  567 

plexuses,  492,  494,  496,  500,  505, 

544 
Choroidal  fissure,  496,  501 
Ciliary  bundle,  253,  272 

ganglion,  338 

processes,  567,  569 

zone,  564,  567 
Cingulum,  483 
Circle  of  Willis,  445,  453 
Circular  sinus,  126,  129 
Circulus  iridis,  571 

tonsillaris,  314 
Circumvallate  papillae,  434 
(  interna  basalis,  443 

magna,  442 

pontis,  443 

arachnoidales,  442 
Claustrum,  514,  519 
Clava,  527 

Clivus  monticuli,  535,  537 
'  lochlea,  560 

membranous,  561 
Collateral  fissure,  465,  467 
( Column  of  Burdach,  177 

of  Goll,  177 
<  lolumn  .  56,  63 

Commissures  of  brain,  504,  505 


Commissures  of  cord,  173 

palpebral,  244 
Concha,  269 

suprema,  398 
Conical  papillae,  434 
Conjunctiva,  245 
Conus  arteriosus,  48 

medullaris,  164,  165 
Convolution.     See  Gyrus 
Cord,    gangliated,    of  sympathetic, 
92,  201,  203.  232.  306,  319 

spinal.     See  Spinal  cord 

vocal,  409,   411,   412,  420,  422, 

43° 
Cords  of  brachial  plexus,  195 

Cornea,  564,  566 
Corneo-scleral  junction,  566 
Cornicula  laryngis,  424 
Cornu  Ammonis,  494 
Cornua  of  grey  matter  of  cord,  174 
of    lateral   ventricles,    490.    491. 

492,  493 
of  thyroid  cartilage,  425 
Corona  radiata,  520 
Coronary  plexus,  51,  74 
sinus,  49,  54 
sulcus,  44 
valve,  54 
Corpora  mammillaria,  454,  456,  498 
quadrigemina,  461,  508 

brachia  of,  508 
Arantii,  60,  75 
Corpus  callosum,  461,  482,  488 
fibres,  486 
genu,  485 
rostrum,  485 
radiation,  486 
splenium,  485,  488 
dentatum,  544 
geniculatum  externum.  504,  508 

internum,  508 
striatum,  464,  514,  517 
trapezoides,  539,  545 
.-mediastinal  sinus,  29 
Cranial  fossa,  middle,  323 
Crescentic  lobule,  535,  536,  537 
'  Iricoid  cartilage,  178,  205,  424.  427 
Cricothyroid   membrane,  178,   205, 

416,  420 
Crista  terminalis,  52 

vestibuli,  559 
Crossed  pyramidal  tract,  177,  524. 

531 
Crura  cerebri,  454,  461,  508,  509 

crusta,  502,  509,  512,  51.) 

tegmentum,  509,  512,  545 


5^4 


INDEX 


Crura  of  crucial  ligament,  361 

Crura  of  stapes,  557 

Crus  helicis,  269 

Crusta,  502,  509,  512,  519 

Crystalline  lens,  564,  575 

Oilmen  monticuli,  535,  536 

Cuneate  funiculus,  527,  529 

nucleus,  529 

tubercle,  527 
Cuneiform  cartilage,  417,  424,  430 

tubercle,  377 
Cuneus,  476 
Cupola  modioli,  561 
Cushion  of  epiglottis,  411 

Eustachian,  373,  3S2 

Decussation  of  fillet,  531 

motor,  531 

of  pyramids,  522,  524 

sensory,  531 
Dentate  fascia,  482 

fissure,  482 

body,  544 
Descemet,  membrane  of,  567 
Diaphragm,  3 
Diaphragma  oris,  296 

sellse,  122,  123 
Diaphragmatic  line  of  pleural  reflec- 
tion, 20 

pleura,  18 
Digastric  triangle,  199,  204 
Dilatator  papillae,  570 
Direct  cerebellar  tract,  177,  525,  528 

pyramidal  tract,  177,  524 
Disc,  intervertebral,  102,  354 

optic,  572 
Drum  of  ear,  547 

Duct,  lymphatic,  right,  90,  216,  224, 
226,  311 

nasal,  276,  278,  397 

parotid,  249,  364 

of  Rivinus,  301,  363,  365 

of  Stenson,  249 

thoracic,  87,  216,  224,  311 

of  Wharton,  298,  301,  363,  365 
Ductus  arteriosus,  59 

cochlearis,  561,  562 

endolymphaticus,  562 
Dura  mater  encephali,  114,  121 
layers,  115 
partitions,  122 

sinuses,  116,  118,  119,  122,  126 
spinal,  159 

Ear,  547 

external,  547 


Ear,  internal,  547,  558 

middle,  547,  550 
Ecto-rhinal  fissure.  468,  478 
Elastic  membrane  of  Descemet,  567 
Eminence,  olivary,  525,  532 
Eminentia  collateralis,  494,  496 
^  teres,  543 
Endocardium,  75 
Endolymph,  547,  558,  562 
Eparterial  bronchus,  33,  80,  90 
Ependyma,  489 
Epicardium,  75 
Epicranial  aponeurosis,  106 
Epiglottis,  376,  410,  431 

cartilage,  424 

cushion,  411 

frenum,  410 
Ethmoidal  cells,  395,  396 
Eustachian  cushion,  373,  382 

orifice,  373 

tube,  371,  373,  381,  550,  558 

valve,  53,  55 
Eyeball,  335,  563 

axis,  563 

chambers,  564,  576 

coats,  564,  565,  567,  570,  572 

equator,  563 

general  structure,  564 

meridional  lines,  563 

poles,  563 

refracting  media,  564,  573,  575 
Eyebrows,  243 
Eye-kernel,  573 
Eyelids,  243,  271 

canthi,  244 

conjunctiva,  245 

glands,  244,  272 

ligaments,  252,  271,  274 

tarsi,  271,  272 

vessels  and  nerves,  276 

Face,  243 

arteries,  266 

muscles,  252 

nerves,  260 

surface  anatomy,  243 
Facial  process  of  parotid,  247 
Falciform  lobe,  465,  481 
Fallopius,  aqueduct  of,  404,  552 
Falx  cerebelli,  122,  123 

cerebri,  119,  122,  461,  462 
Fascia,  bucco-pharyngeal,  368 

bulbi,  345 
Fascia,  cervical,  182,  188,  208 

dentate,  482 

lumbar,  140 


INDEX 


585 


Fascia,  parotid,  185,  248,  249 

phrenico-pleural,  23 

pretracheal,  186,  208 

prevertebral,  186 

of  Sibson,  16,  23,  226 

temporal,  112,  280 
Fasciculus  teres,  543 
Fauces,  isthmus  of,  362,  366,  373,  375 

pillars,  366,  375 
Fenestra  ovalis,  552,  559 

rotunda,  553 
Fibrse  arcuatse,  528,  531,  533 
Fifth  ventricle,  497 
Fillet,  514,  531,  533 

decussation,  531 

lateral,  514,  545,  546 

mesial,  514,  545,  546 
Filum  terminate,  160,  164 
Fimbria,  482,  483,  494,  495,  499 
Fissure  or  Fissures,  calcarine,  476 

calloso-marginal,  465,  468 

of  cerebellum,  535 

of  cerebrum,  462,  463,  465 

choroidal,  496,  501 

collateral,  465,  467 

dentate,  482 

ecto-rhinal,  468,  478 

great  horizontal,  535 
longitudinal,  461,  462 

of  lung,  30 

of  medulla,  522 

oral,  362 

palpebral,  243 

parieto-occipital,  465,  467 
external,  467 
internal,  467 

of  Rolando,  465,  466 

sphenoidal,  343 

of  spinal  cord,  172 

of  Sylvius,  462,  465 

transverse,  496,  501 
Flocculus,  538 

Fold,    aryteno  -  epiglottidean,    376, 
411 

glosso-epiglottidean,  410,  425 

pharyngo-epiglottidean,  410,  425 

salpingopharyngeal,  373 

tympano-malleolar,  554 

vestigial,  38 
Folium  cacuminis,  535,  537 
Fontana,  spaces  of,  567 
Foramen  caecum  of  medulla,  522 
of  tongue,  432 

of  Magendie,  544 

of  Monro,  461,  490,  506 

ovale,  55,  62 


Foramina  Thebesii,  51,  54,  62 
Forceps  major,  486 
Formatio  alba,  532 

grisea,  532 

reticularis,  513,  529,  532 
Fornix,  497,  498 

of  conjunctiva,  245 
Fossa  of  antihelix,  270 

cranial,  middle,  323 

of  helix,  270 

nasal,  386,  391 

ovalis,  54 

patellaris,  573 

pyriformis,  376 

rhomboidalis,  522 

of  Rosenmuller,  374 

scaphoid,  270 

spheno-maxillary,  383,  401 

supra-sternal,  178 

supra-tonsillar,  376 

triangularis  pinnae,  270 
Fourth  ventricle,  460,  521,  541 
floor,  522,  531,  541 
lateral  recesses,  541 
roof,  541,  543 
Fovea  centralis  retinas,  573 

hemi-elliptica,  559 

hemispherica,  559 

inferior,  542 

superior,  543 
Frenulum  of  Giacomini,  482 

of  lips,  363 

veli,  508 
Frenum  of  epiglottis,  410 

linguae,  365,  433 
Frontal  lobe,  465,  468 

operculum,  466,  471 

pole,  462 

sinus,  396 
Fronto-parietal     operculum,      466, 

470 
Fungiform  papillae,  434 
Funiculus  cuneatus,  527,  529 

gracilis,  527,  529 

of  Rolando,  527,  531 
Furrowed  band,  539 

( ralen,  veins  of,  500 

Gangliated  cord  of  sympathetic,  92, 

201,  203,  306,  319 
Ganglion,  basal,  514 

cervical,  inferior,  216,  321 

middle,  2l6,  321 

superior,  319 
ciliary,  338 
Gasserian,  323,  325 


586 


INDEX 


Ganglion,  geniculate,  405,  406 

jugular,  of  glossopharyngeal,  314 
of  vagus,  315 

lenticular,  331,  336,  337,  338,  343 

of  Meckel,  385,  401 

nodosum,  315 

otic,  291,  294,  386 

ophthalmic,  336 

petrous,  314 

of  root  of  vagus,  315 

sphenopalatine,  401 

spinal,  166,  168 

spirale,  561 

splanchnic,  93 

submaxillary,  298,  302 

of  trunk  of  vagus,  315,  316 

of  Wrisberg,  35 
Gasserian  ganglion,  323,  325 
Geniculate  bodies,  504,  508 

ganglion,  405,  406 
Genu  of  corpus  callosum,  485 

of  fissure  of  Rolando,  467 

of  internal  capsule,  519 
Giacomini,  frenulum  of,  482 
Glenoid  lobe,  248 
Globus  pallidus,  518 
Glosso-epiglottidean  folds,  410,  425 
Glottis,  false,  411 

respiratoria,  412 

vera,  412,  422 

vocalis,  412 
Goll,  column  of,  177 
Gracile  funiculus,  527,  529 

lobule,  539 

nucleus,  527,  529 
Grey  commissure,  504,  505 
Groove,  aortic,  29 

auriculo-ventricular,  44,  66 

interventricular,  48 
Gullet,  84,  200,  242 
Gums,  364 
Gyrus  or  Gyri,  463 

angular,  475 

callosal,  481 

central,  474 

cunei,  476 

cuneo-lingual,  476 

dentatus,  482 

fornicatus,  481 

of  frontal  lobe,  469 

frontal,  469,  470 

hippocampal,  481 

lingualis,  476 

marginalis,  472 

occipitotemporal,  476,  479 

orbital,  472 


Gyrus  or  Gyri,  parietal,  473.  474 
post-parietal,  475 
rectus,  472 
sub-callosus,  480 
supra-callosus,  485 
supra-marginal,  475 
temporal,  478 

Head  and  Neck,  104 
auditory  apparatus,  547 
brain,  112,  439 
carotid  canal,  382 
cranial  cavity,  113,  323 
eyeball,  335.  563 
face,  243 
joints,  287,  353 
larynx,  200,  408 
mouth  and  pharynx,  362,  431 
movements,  361 
nasal  fossae,  386,  391 
neck,  132,  304 
orbit,  330 

prevertebral  region,  348 
pterygo-maxillary  region,  279 
scalp,  104 

submaxillary  region,  295 
temporal  region,  278 
Heart,  10,  40 
action,  64 
annulus  ovalis,  55 
aortic  orifice,  63,  64,  67,  78 

valve,  63,  64,  74 

vestibule,  64 
apex,* 41,  66 
atrium,  46 

auricles,  43,  45,  52,  61,  64 
auricular  appendices,  45,  46,  61 
auriculo-ventricular  apertures,  44, 
54,  56,  57,  61,  63,  67,  76 

bundle,  76 

groove,  44,  66 

rings,  77 
base,  40,  41,  45 
bicuspid  valve,  63 
chordae  tendineae,  56,  63,  64 
columnar  carneae,  56,  63 
conus  arteriosus.  48 
coronary  sinus,  49,  54 
crista  terminalis,  52 
endocardium,  75 
epicardium,  75 
Eustachian  valve,  53,  55 
external  form,  43 
foramen  ovale,  55,  62 
foramina  Thebesii,  51,  54,  62 
fossa  ovalis,  54 


INDEX 


5*7 


Heart,  general  relations,  41 

infundibulum,  48 

interauricular  sulcus,  45 

interventricular  sulcus,  48 

margo  acutus,  48,  66 
obtusus,  48,  66 

mitral  valve,  63 

moderator  band,  56 

musculi  papillares,  56.  63 
pectinati,  52,  61 

myocardium,  75 

nerves,  34,  51,  72 

pars  membranacea  septi,  64 

pulmonary  orifice,  56,  66,  78 
valve,  60 

semilunar  valves,  57,  74 

septum  atriorum,  54 
ventriculorum,  64 

sulcus  terminalis,  45,  52 

surfaces,  41,  48 

Thebesian  valve,  54 

topography,  65 

tricuspid  valve,  57 

tubercle  of  Lower,  55 

ventricles,  43.  47,  55,  62,  76 

vessels,  49 

wall,  75 
Helicotrema,  561 
Helix,  269 

fossa,  270 

spine,  270 
Hemisphere,  cerebellar,  534 

cerebral.       See    Cerebral     hemi- 
spheres 
Heschl,  sulci  of,  478 
Hiatus  semilunaris,  396 
Highmore,  antrum  of,  396 
Hippocampus  major,  494 

minor,  493 

pes,  494 

taenia,  495 
Horner,  muscle  of,  252 
Huguier,  canal  of,  408 
Hyaloid  canal,  574 

membrane,  574 
Hyparterial  bronchi,  33,  80,  90 
Hypophysis  cerebri,  132 

Incisive  bundle,  259 

pad,  366 
[ncisor  teeth,  365 
[ncisura  cardiaca,  \o 

intertragica,  270 
ilunaris,  534 
temporalis,  468,  47S 

tentorii,  122 


Incisura  thyroidea,  425 

Incus,  555 
Infra-orbital  canal,  ^8^ 

plexus,  264 
Infundibular  cusp,  58 
Infundibulum    of   brain,    120,    132, 

454,  456>  5°7 

of  heart,  48 

of  nose,  396 
Insula,  465,  480,  493 

opercula  of,  466,  471 
Interarticular  fibro-cartilage,  214 
Interauricular  furrow,  45 
Interbrain,  461 
Intercavernous  sinuses,  129 
Intercostal  lymphatic  glands,  89 

membranes,  5,  94 
Internal  capsule,  502,  519 

ear,  547,  558 
Interpeduncular  space,  454 
Interventricular  grooves,  48 
Intervertebral  discs,  102,  354 
Iris,  564,  567,  570 
Island  of  Reil,  465,  480,  493 
Isthmus  of  auditory  meatus,  547 

of  callosal  gyrus,  481 

of  Eustachian  tube,  382 

of  fauces,  362,  366,  373,  375 

of  limbic  lobe,  481 

of  pharynx,  374 

of  thyroid  gland,  207,  240 
Iter  chordce  posterius,  407 

Jacobson's  nerve,  314 

organ,  389 
Joints,  atlanto-axial,  356 

atlanto-occipital,  357 

capitular,  99,  100 

costo-transverse,  100,  10 1 

costo-vertebral,  99 

crico-arytenoid,  430 

crico-thyroid,  426 

interchondral,  99 

intervertebral,  101,  353 

manubrio-glandiolar,  98 

sterno-chondral,  98 

sterno-clavicular,  212 

temporo-maxillary,  287 

of  thorax,  97 
Jugular  ganglion,  314 

Labial  glands,  259,  363 
Labyrinth,  n  1  us,  547,  55S. 

562 
osseous,  547,  558 
Lachrymal  apparatus,  276 


588 


INDEX 


Lachrymal  canals,  276,  277 

gland,  276,  331,  334 

sac,  276,  278 
Lacuna;  laterales,  115,  119 
Lacus  lacrimalis,  244 
Lambda,  113 
Lamina  cinerea,  456 

cribrosa  of  eye,  565 

fusca,  575 

spiralis,  561 
Lamina?,  medullary,  518 
Laryngectomy,  208 
Larynx,  200,  408 

cartilages,  424 

glottis,  411,  412,  413,  422 

interior,  409 

mucous  membrane,  414 

position,  408 

saccule,  414 

sinus,  414,  422 

superior  aperture,  37^,  37&,  410 

vestibule,  409 

vocal  cords,  409,  411,  412,  420, 
421,  422,  430 
Lateral  recesses  of  fourth  ventricle, 

541,  543 
of  pharynx,  374 
sinus,  122,  126,  128 
sulcus  of  mesencephalon,  510 
ventricles,  461,  487 
body,  490,  491 
cornua,  490,  493 
trigone,  493 
Lemniscus,  531 
Lens,  564,  575 
Lenticular  ganglion,  331,  336,  337, 

338,  343 
nucleus,  514,  516 
Ligaments,  alar  odontoid,  357,  361 
atlanto-axial,  357,  359 
atlanto-occipital,  357,  358,  359 
of  auditory  ossicles,  557 
auricular,  270 
capitular,  100 
central,  of  cord,  164 
check,  357,  361 

of  orbit,  346 
common,  of  spine,  102,  355 
costo-clavicular,  213 
costotransverse,  101 
cruciform,  357,  360 
epiglottidean,  424 
hyo-epiglottidean,  425 
of  incus,  557 
interclavicular,  213 
internal  lateral,  of  jaw,  283 


Ligaments,  interspinous,  101,  356 

intertransverse,  101,  103,  356 

intervertebral,  101,  102,  354 

of  malleus,  557 

occipito-atlantal,  357 

occipito-axial,  357,  359 

palpebral,  273 

of  pinna,  270 

pterygo-maxillary,  370 

rhomboid,  213 

of  stapes,  557 

stellate,  100 

sterno-chondral,  98 

sterno-clavicular,  213 

sterno-pericardiac,  35 

stylo-hyoid,  299,  305 

stylo-maxillary,  186,  187,  287 

supraspinous,  101,  356 

suspensory,  of  axis,  357,  361 
of  lens,  574 
of  orbit,  346 

tarsal,  of  eyelids,  252,  274 

temporo-maxillary,  287 

thyro-arytenoid,  421,  422 

thyro-epiglottidean,  425 

thyro-hyoid,  415 

transverse,  of  atlas,  360 
Ligamentum  arteriosum,  59,  70 

cava;  sinistra;,  38 

denticulatum,  163,  165 

latum  pulmonis,  10,  16 

nucha;,  147 

pectinatum  iridis,  567 
Ligamenta  subflava,  101,  355 
Ligula,  543 
Limbic  lobe,  465,  481 
Limbus  fossa;  ovalis,  55 
Line,  mammillary,  22 

mid-lateral,  22 
Linea  splendens,  163,  165 
Lines  of  pleural  reflection,  18 
Lingual  glands,  436 
Lingula,  535,  536,  541 
Lips,  363 
Lobe  or  Lobes,  of  cacumen,  537 

central,  of  cerebellum,  535,  536 
of  cerebrum,  465 

cerebellar,  535 

cerebral,  465,  469,  472,  477,  480 

ofclivus,  537 

of  culmen,  536 

falciform,  465,  481 

frontal,  465,  46S 

glenoid,  248 

insular,  465,  480 

limbic,  465,  481 


INDEX 


589 


Lobe  or  Lobes,  of  lung,  30 

of  nodulus,  539 

occipital,  465,  475 

olfactory,  465,  480 

optic,  508 

palpebral,  334 

parietal,  465,  472 

of  pyramid,  539 

pyramidal,  240 

temporal,  465,  477 

of  tuber,  539 

of  uvula,  539 
Lobule  or  Lobules,  biventral,  538 

central,  of  cerebellum,  535,  536 

crescentic,  535,  536,  537 

of  ear,  269 

gracile,  539 

paracentral,  472 

parietal,  475 

quadrate,  473,  537 
Locus  cceruleus,  543 

perforatus  anticus,  456 
posticus,  455 
Longitudinal  bundle,  posterior,  513, 

533,  545,  546 
sinus,  inferior,  119,  126,  127 
superior,  118,  119,  126,  127 
Lower,  tubercle  of,  55 
Lumbar  fascia,  140 
Lung,  10,  25 
apex,  26 
base,  26,  27 
borders,  29 
bronchi,  31,  32,  90 
cardiac  notch,  30 
differences  between  right  and  left, 

29 
lissures,  30 
liilum,  28 

ligamentum  latum,  II,  16 
lobes,  30 
pedicle,  10 
root,  10,  30 
surfaces,  27 
sulci,  26,  29 
Lunula?,  75 

Lymphatic   duct,    right,    90,    216, 
224,  31  ] 
glands,  bronchial,  31,  89 
cervical,  181,  188,  201,  204 
intercostal,  89 
mediastinal,  89 
parotid,  24S 

rnal,  89 
submaxillary,  204 
suprahyoid,  205 


Lymphatic  glands  of  thorax,  89 
Lyra,  499 

Macula  lutea,  573 
Magendie,  foramen  of,  544 
Malleus,  555 

Mammillary  bodies,  454,  456 
Mandibular  canal,  295 
Manubrium  mallei,  555 
Marginal  cusp,  58,  64 
Marshall,  oblique  vein  of,  50 

vestigial  fold  of,  38 
Mastoid  antrum,  549 

cells,  549 
Meatus,  auditory,  external,  547 
auditory,  internal,  404 
of  nose,  inferior,  397 
middle,  395 
superior,  395 
Meckel's  ganglion,  385,  401 
Mediastinal  lymphatic  glands,  89 
pleura,  16 
space,  23 
Mediastinum,  11,  23 
anterior,  12,  24 
middle,  24 
posterior,  24,  80 
superior,  24 
Medulla  oblongata,  439,  460,  521 
arcuate  fibres,  528,  531,  533 
areas,  523,  525,  526 
central  canal,  522,  531 
closed  part,  522 
decussation  of  pyramids,   522, 

524 
direct  cerebellar  tract,  525 

fillet,  53i>  533 

floor  of  fourth  ventricle,   522, 

53i>  54i 
formatio  reticularis,  529,  532 
fossa  rhomboidalis,  522 
funiculus  cuneatus,  527,  529 

gracilis,  527,  529 

Rolandi,  527,  531 
furrows,  522 
grey  matter,  529,  532 
internal  structure,  529 
nuclei,  527,  531,  532 
olivary  eminence,  525,  526,  532 
open  part,  522 
origin  of  nerves,  522 
pyramidal  tract,  524,  531 
pyramids,  523 
raphe,  529 

restiform  body,  460,  527 
tubercle  of  Rolando,  527,  531 


59° 


INDEX 


Medulla    oblongata,   white   matter, 

529 
Medullary  centre,  463 

lamince,  518 

vela,  535,  539,  540,  543 
Meibomian  follicles,  244,  272 
Membrana  fiaccida,  554 

tectoria,  359 

tympani,  547,  553,  562 
secondary,  553,  562 
Membrane,  crico-thyroid,  178,  205, 
416,  420 

of  Descemet,  567 

hyaloid,  574 

intercostal,  4,  5,  94 

nictitating,  245 

of  Shrapnell,  554 

thyro-hyoid,  205,  415 
Meninges  of  brain,  114,  441 

of  cord,  159 
Mesencephalon,  461,  507 
Mid-brain,  461 
Middle  ear,  547,  550 
Mitral  valve,  63 
Moderator  band,  56 
Modiolus,  561 
Molar  glands,  363 

teeth,  365 
Moll,  glands  of,  273 
Monro,  foramen  of,  461,  490,  506 
'   sulcus  of,  507 
Monticulus,  534 
Morgagni,  sinus  of,  371 
Motor  decussation,  531 
Mouth,  362 

floor,  365 

roof,  365 

tongue,  431 

vestibule,  362 
Muscle  or  Muscles,  accessorius,  143. 
144 

antitragus,  271 

aryteno-epiglottidean,  418 

arytenoid,  417,  431 

ary-vocalis,  420,  431 

attollens  auriculam,  107 

attrahens  auriculam,  107 

azygos  uvula?,  379,  380 

biventer  cervicis,  147 

broncho-cesophageal,  So 

buccinator,  257,  363 

cervicalis  ascendens,  144 

chondro-glossus,  436 

ciliary,  567,  569 
of  eyelid,  272 

complexus,  146,  194 


Muscle     or     Muscles,     compressor 

naris,  260 
constrictor  pharyngis,  368 
corrugator  supercilii.  253 
crico-arytenoid,  417,  418,  431 
crico-thyroid,  206,  415,  430 
depressor  alae  nasi,  260 

anguli  oris,  254,  256 

labii  inferioris,  257 
digastric,  198,  205,  210 
dilator  naris,  260 

pupilke,  570 

tubae,  382 
of  ear,  extrinsic,  106,  270 

intrinsic,  270,  271 
erector  spina?,  143 
of  face,  252 

genio-hyoglossus,  297,  304,  436 
genio-hyoid,  297,  300 
helicis  major,  271 

minor,  '271 
of  Horner,  252 
hyoglossus,  297,  299,  436 
ilio-costalis,  143 
incisivus,  259 
infra-hyoid,  209 
interaccessorii,  153 
intercostal,  4,  93,  94 
interspinales,  153 
intertransversales,  153,  348,  351 
of  jaw-movements,  289 
of  laryngeal  movements,  430 
latissimus  dorsi,  3 
levator  anguli  oris,  256,  259 
scapulae,  138,  194 

glanduke  thyroidece,  206,  240 

labii  superioris,  256 

levator  labii  superioris  alaeque 
nasi,  256 

menti,  259 

palati,  371,  379,  380 

palpebral  superioris,  276,  330. 

334 

proprius  alae  nasi,  260 
levatores  costarum,  153 
linguales,  436 
longissimus  capitis,  144 

dorsi,  143,  144 
longus  colli,  349 
masseter,  280 
of  mouth,  253 
multifidus  spinie,  151,  152 
mylo-hyoid,  205,  296 
naso-labialis,  259 
of  nose,  260 
obliquus  auricula;,  271 


INDEX 


59i 


Muscle  or  Muscles,  obliquus  capitis, 
156 

externus  abdominis,  3 

inferior,  of  neck,  156 
of  orbit,  330,  344 

superior,  of  neck,  156 
of  orbit,  330,  335 
occipito-frontalis,  105 
omo-hyoid,    138,    190,    198,    206, 

209,  216 
orbicularis  oris,  254,  258 

palpebrarum,  252,  272 
palato-glossus,  378,  380,  436 
palato-pharyngeus,  375,  378,  380 
papillary,  of  heart,  56,  63 
pectinati,  52,  61 
pectorales,  3 
platysma,  179,  180,  205 
pleuro-cesophageal,  81 
prevertebral,  348 
pterygoid,  282,  284,  289 
pyramidalis  nasi,  260 
rectus  abdominis,  3 

capitis  anticus,  350,  351 
lateralis,  306,  322 
posticus,  156 

externus,  330,  342 

inferior,  330,  342 

interims,  330,  342 

superior,  330,  335,  342 
retrahens  auriculam,  107 
of  Riolan,  272 
risorius,  246,  254,  255 
rotatores  spinas,  151,  152 
salpingo-pharyngeus,  379 
scalenus  anticus,  193,  216 

medius,  194,  216 

posticus,  4,  194,  216,  217 
semispinalis  colli,  151,  152 

dorsi,  151,  152 
serratus  magnus,  3,  194 

posticus,  inferior,  139 

posticus,  superior,  139 
sphincter  pupilke,  570 
spinalis  dorsi,  143,  145 
splenius  capitis,  142,  194 

colli,  142 
stapedius,  551,  557 
sternohyoid,  200,  206,  208,  209 
sterno-mastoid,  136,  187,  198 
sternothyroid,  200,  206,  208,  210 
stylo-glossus,  297,   299,  436 
stylo-hyoid,  198,  21 1 
stylo-pharyngeus,  306 
subcostalis,  94 
subclavius,  4 


Muscle  or  Muscles,  temporal,  281 
tensor  palati,  371,  379,  380,  402 

tarsi,  252,  276,  278 

tympani,  552,  557 
thyro-arytenoid,  419,  431 

externus,  419 

internus,  420 

superior,  420 
thyro-epiglottidean,  420 
thyro-hyoid,  206,  2IO 
of  tongue,  435 
trachelo-mastoid,  144 
tragicus,  271 

transversalis  cervicis,  144 
transversus  auriculae,  271 

spinalis,  15 1 

of  tongue,  437 
trapezius,  136,  189 
triangularis  sterni,  7,  10 
of  tympanic  cavity,  557 
vertical,  of  tongue,  437 
zygomaticus  major,  254 

minor,  256 
Muscular    triangle    of    neck,    199, 

200 
Myocardium,  75 

Nares,  posterior,  ^j^ 
Nasal  cartilages,  278 

duct,  276,  278,  397 

fossa,  386,  391 
atrium,  394 
inferior  meatus,  397 
infundibulum,  396 
middle  meatus,  395 
olfactory  part,  388,  398 
outer  wall,  393,  398,  399 
recessusspheno-ethmoidalis,  397 
respiratory  part,  388,  398 
superior  meatus,  395 
turbinated  bones,  393,  395,  398 
vestibule,  393 

septum,  387,  389,  390 
Naso-labial  band,  259 
Naso-pharynx,  373 
Neck,  104 

anterior  triangle,  178,  198 

deep  dissection,  306 

digastric  triangle,  199,  204 

carotid  triangle,  199,  201 

fascke,  179,  182,  188,  208 

infra-hyoid  region,  205 

joints,  353 

mid-line,  205 

muscular  triangle,  199,  200 

occipital  triangle,  190,  193 


592 


INDEX 


Neck,  posterior  triangle,  137,    178, 
187,  189,  193 

side  of,  178 

submaxillary  triangle,  199,  295 

submental  triangle,  205 

supraclavicular  region,  188,  191 
triangle,  190,  191,  194 

suprahyoid  region,  205 

surface  anatomy,  133,  178 

surgical  anatomy,  208 
Nerve  or  Nerves,  abducent,  120, 126, 
323,  328,  331,  343,  456,  458 

acromial,  182,  228 

anterior  cutaneous,  4,  6 

aortic,  92 

of  Arnold,  262,  315 

auditory,  120,  126,  404,  408,  456, 

458 
auricular  of  auriculotemporal,  293 

great,  134,  136,  182,  228 

of  great  occipital,  ill 

posterior,  no,  262 

of  small  occipital,  no 

of  vagus,  262,  315 
auriculotemporal,  no,  261,  283, 

292,  293 
to  azygos  uvuloe,  380 
brachial,  191,  195,  216 
buccal,  261,  266,  283,  291,  292 

of  facial,  264 
cardiac,  34,  51,  73,  74,  320>  321 

of  vagus,  35,  73,  84,  317 
carotid,  external,  320 
carotico-tympanicus,  315,  383 
cervical,  137,   166,  181,  195,  227, 
321,  322,  348,  351,  458,  522 

posterior    divisions,    134,    137, 

148,  351 

superficial,  182,  198,  228 
cervicalis  descendens,  21 1, 228, 229 
chorda  tympani,  297,404,551,  558 
clavicular,  182,  228 
ciliary,  336,  337,  338,  566,  571 
coccygeal,  154,  166 
cochlear,  408,  458,  561 
cranial,  123,  456 

deep  origin,  456 

exits  from  cranium,  124 

nuclei,  457 

superficial  origin,  456,  522,  533 
dental,  inferior,  283,  292,  293,  295 

superior,  385 
descendens  hypoglossi,  201,  203, 

211,  229,  232 
to  digastric,  204,  211,  262,  294 
dorsal,  95,  149,  166,  195 


Nerve  or  Nerves,  external  respiratory 
of  Bell,  196,  197 

of  face,  261 

facial,  120,  126,  250,  254,  261,  456 
cervical  division,  184,  198,  262 
cervico-facial  division,  261,  264 
of  great  auricular,  136,  246,  261 
intrapetrous  part,  404 
pars  intermedia,  120,  126,  458 
superficial  origin,  458 
temporo-facial  division,  261 ,  263 

frontal,  328,  331,  333,  343 

glosso-pharyngeal,  120,  126,  299, 

306,  312,  313,  437,  456,  532 
jugular  ganglion,  315 
petrous  ganglion,  314 
superficial  origin,  458,  522 

of  heart,  34,  51,  72 
hypoglossal,    120,   126,   201,   203, 
204,  211,  298,  303,  306,  318, 

438,  456,  531 

superficial  origin,  457,  522 
incisor,  295 
infra-mandibular,  264 
infra-orbital,   256,  261,  264,  265, 

276,  384 
infra  -  trochlear,    261,    265,    276, 

337 
intercostal,  5,  95 
intercosto-humeral,  6,  95  • 
of  Jacobson,  314 
labial,  266,  385 

lachrymal,  276,  32S,  331,  ^j,  343 
laryngeal,  external,  200,  201,  203, 

307,  3i6 

internal,    201,    203,    307,    316, 

423,  438 
recurrent,   84,    200,    232,    317, 

416,  423 
superior,  307,  316 
lateral  cutaneous,  4,  6 
to  levator  palati,  380 
lingual,  283,  292,  294,   298,   302, 

438 

of  ninth,  314 

of  vagus,  318 
lumbar,  150,  166 
malar,  261,  263,  265,  347 
mandibular,  264,  283 
masseteric,  283,  291,  292 
mastoid,  no,  136 
maxillary,  inferior,  266,  290,  326, 

327' 
superior,  265,  326,  327,  383 
meningeal,    168,    315,    319,    327, 
329 


INDEX 


593 


Nerve  or  Nerves,  mental,  256,  261, 
266,  295 
mylohyoid,  204,  292,  294 
nasal,    261,    265,  266,   328,   331, 

336,  337,  343,  385,  399,  400 
inferior,  399,  400,  403 
superior,  391,  399,  402 
of  Vidian,  391,  404 
naso-palatine,  390,  399,  402 
occipital,  great,  no,  134,  149 
of  posterior  auricular,  no 
small,  no,  134,  135,   182,  189, 

228 
third,  135 
oculo-motor,  120,  124,  323,   328, 

33i,  343,  455,  456,  459 
oesophageal,  84,  317 
olfactory,  119,  124,  390,  399,  456, 

460 
to  omo-hyoid,  188,  209,  212 
ophthalmic,  264,  326,  327 
optic,  119,  124,  336,  456,  565,  572 

superficial  origin,  454,  459 
orbital,  331,  347,  385,  403 
to  palate,  380 

palatine,  posterior  accessory,  380, 
402 

great,  402 

small,  380,  402 
palpebral,  261,  265,  266,  385 
pericardiac,  34,  84 
petrosal,  external  superficial,  320, 

330,  407 
great  deep,  329,  383 

superficial,  323,  329,  383,407 
small  deep,  314,  383 

superficial,    314,    323,    330, 

387 
pharyngeal,  403 

of  glosso-pharyngeal,  313 

of  sympathetic,  320 

of  vagus,  307,  316 
phrenic,  25,  33,  189,  216,  228,  229 
pneumogastric.    See  Nerve,  Vagus 
posterior  thoracic,  196,  197 
pterygoid,  290,  291,  292 
pulmonary,  31,  92 
recurrent,  of  hypoglossal,  319 

of  inferior  maxillary,  290 

of  superior  maxillary,  327,  385 

of  vagus,  315 
to  rhomboids,  137,  196 

ral,  153,  166 
of  scalp,  107,  134 

tal,  39°>  391.  399 
gpneno- palatine,  385,  401 

VOL.  n  —38 


Nerve  or  Nerves,  spinal,  165 

anterior  primary  divisions,  169 

classification,  166 

exits  from  spinal  canal,  167 

ganglia,  166,  168 

origin  from  cord,  166,  171 

posterior  primary  divisions,  148, 

169 
roots,  166 
spinal  accessory,   120,   126,    137, 
191,  201,  203,  306,  312,  317, 
456 
accessory  part,  317 
spinal  part,  317,  458 
superficial  origin,  458,  522 
splanchnic,  92 
great,  92 
small,  92 
smallest,  92 
to  stapedius,  407 
sternal,  182,  228 
stylo-hyoid,  263 
to  stylo-pharyngeus,  313 
to  subclavius,  189,  196,  197 
sub-occipital,  148,  156,  166,  167, 

322,  351 
supraclavicular, of  brachial  plexus, 

196 
supra-orbital,  109,  261,  265,  276, 

55 

supra-scapular,  139,  196,  197 
supra-trochlear,     107,    261,    265, 

276,  333 

sympathetic.     See  Sympathetic 

temporal,  of  buccal,  293 
deep,  283,  291,  292 
of  facial,  109,  263 
of  orbital,  109,  261,  263 
of  superior  maxillary,  347 

temporo-malar,  280,  347,  385 

to  tensor  palati,  380,  387 
tympani,  387 

thyroid,  321 

thyrohyoid,  200,  201,  203,  212 

tonsillitic,  314 

to  trapezius,  137,  191,  228,  229 

trigeminal,  120,  125,  325,  456 
Gasserian  ganglion,  323,  325 
motor  root,  321,  325,  327,  459 
sensory  root,  321,  325,  459 
spinal  root,  527 
superficial  origin,  458,  533 

trochlear,  120,  125,  323,  328,  331, 

335:  343,  456,  459,  5ii 
superficial  origin,  459 
tympanic,  314 


594 


INDEX 


Nerve  or   Nerves,   vagus,   81,    120, 
126,201,  203,  306,  312,  315, 

456,  532 
ganglion  of  root,  315 

of  trunk,  315 
left,  82 
right,  82 
superficial  origin,  458,  522 

vestibular,  408,  458 

Vidian,  330,  383,  403 
Nictitating  membrane,  245 
Nodule  of  cerebellum,  538 
Nose,  cartilages  of,  278 

fossae.     See  Nasal  fossae 

septum,  387,  389 

vestibule,  388 
Nostril,  391 
Nucleus,  457 

amygdaloid,  493,  514 

auditory,  542,  545 

caudate,  491,  493,  514,  515 

cuneate,  527,  529 

glossopharyngeal,  532,  542 

gracilis,  527,  529 

hypoglossal,  531,  542 

of  lens,  576 

lenticular,  514,  516 

oculo- motor,  511 

olivary,  532 
accessory,  532 

of  optic  thalamus,  520 

pontis,  545 

pulposus,  103 

red,  514 

trigeminal,  511 

trochlear,  511 

vagus,  532,  542 
Nuchal  furrow,  134 
Niihn,  gland  of,  436 

Obex,  543 

Oblique  sinus  of  pericardium,  38 
Obliterated  ductus  arteriosus,  59 
Occipital  lobe,  465,  475 

pole,  462 

sinus,  126,  127 

triangle,  190,  193 
GEsophageal  plexus,  80 
CEsophagus,     84,     200,     242,    373, 

377 
Olfactory  bulb,  441,  480 

lobe,  465,  480 

peduncle,  441 

tract,  480 

trigone,  480 
Olivary  eminence,  525,  532 


Olivary  nucleus,  532 

peduncle,  532 
Olive,  superior,  546 
Opercula  insula?,  466,  471 
Ophthalmic  ganglion,  336 
Optic  chiasma,  454 

disc,  572 

entrance,  565 

lobes,  508 

thalamus,  461,  492,  502,  520 

tract,  454 
roots  of,  509 
Ora  serrata,  572 
Oral  fissure,  362 
Orbit,  330 
Orbital  septum,  273 

operculum,  466,  471 

periosteum,  331 
Organ  of  Jacobson,  389 
Ossicula  auditus,  547,  555,  562 
Otic  ganglion,  291,  294,  386 

Pacchionian  bodies,  114,  119,  444 
Palate,  hard,  365 

soft,  365,  377 
Palatal  aponeurosis,  380 
Palatine  papilla,  366 
Palpebral,  243,  271 
Palpebral  commissures,  244 

conjunctiva,  245 

fissure,  243 

lobe  of  lachrymal  gland,  334 
Papilla  foliata,  433 

lacrimalis,  244 

palatina,  366 
Papillae,  circumvallate,  434 

conical,  434 

fungiform,  434 
Paracentral  lobule,  472 
Paramedian  sulcus  of  cord,  177 

of  cerebrum,  470 
Parasinoidal  sinuses,  115 
Parietal  lobe,  465,  472 

lobule,  475 
Parieto-occipital  fissure,  465,  467 
Parotid  duct,  249,  364 

fascia,  185,  248,  249 

gland,  204,  246 

lymphatic  glands,  248 
Pars    basilaris    of    inferior    frontal 

gyrus,  470 
Pars  ciliaris  retinae,  572 

intermedia  of  Wrisberg,  120,  126, 
458 

iridica  retinae,  572 

membranacea  septi,  64 


INDEX 


595 


Pars    orbitalis    of    inferior     frontal 

gyrus,  470,  471 
triangularis     of     inferior    frontal 

gyrus,  466,  470,  471 
Peduncles  of  cerebellum,  460,  461, 

513,  528,  533,  535,  540,  545, 
546 
olfactory,  441 
olivary,  532 
of  pineal  body,  505 
Pericardium,  10,  35 
fibrous,  27 
oblique  sinus,  38 
parietal,  37 
serous,  37 
transverse  sinus,  38 
vestigial  fold,  38 
visceral,  37 
Perichoroidal  space,  565 
Perilymph,  547,  558,  561,  562 
Pes  anserinus,  263 
of  crus  cerebri,  509 
hippocampi,  494 
Petit,  canal  of,  575 
Petrosal  sinus,  inferior,  126,  129,  311 

superior,  122,  126,  129 
Petro-squamous  sinus,  129 
Petrous  ganglion,  314 
Pharyngeal  aponeurosis,  371 
bursa,  374 

plexus,  316,  318,  368 
tonsil,  366,  372,  374 
Pharyngo-epiglottidean  folds,   410, 

425 
Pharynx,  201,  348,  362,  366 
bucco-pharyngeal  fascia,  368 
constrictor  muscles,  368 
glands,  372 
interior,  371 
isthmus,  374,  375 
laryngeal  part,  373,  376 
lateral  recesses,  374 
lymphoid  follicles,  372 
nasal  part,  373 
openings,  372,  375,  376 
-.ml  part,  373,  375 
roof,  374 
tonsil,  366,  372,  376,  381 

pharyngeal,  372,  374 
veins,  368 

walls,  367,  273,  374 
Phrenico- pleural  fascia,  23 
Pia  mater  encephali,  114,  444 

spinalis,  159,  163 
Pillars  of  fauces,  366,  375 
fornix,  49X 


Pillars  of  iris,  567 
Pineal  body,  504 
Pinna,  269,  547 
Pituitary  body,  132 
Pleura,  7,  11 

cervical,  16,  216,  226 

costal,  11 

diaphragmatic,  18 

lines  of  reflection,  18 

mediastinal,  16 

parietal,  1 1 

relations,  13 

visceral,  11,  14 
Pleural  cavities,  11 

sac,  11,  18 
Plexus,  brachial,  191,  195 

buccal,  292 

cardiac,  deep,  72,  y^ 
superficial,  34,  72 

carotid,  320,  383 

cavernous,  323,  329,  3S3 

cervical,  226,  306,  322 

communicating  branches,  229 
muscular  branches,  228 
superficial  branches,  181,  191, 
228 

choroid,    492.    494,     496,     500, 

505,  544 
coronary,  of  heart,  51,  74 
gulae,  82,  83,  84 
hypogastric,  72 
infra-orbital,  264 
intraspinal  venous,  158 
oesophageal,  82 
parotideus,  263 
pharyngeal,  316,  318,  368 
pterygoid,  venous,  286 
pulmonary,  31,  32,  82,  83 
solar,  72 

spinal,  venous,  154 
subclavian,  321 
subtrapezial,  229 
tympanic,  558 
Plica  sublingualis,  301,  362 
fimbriata,  433 
semilunaris,  245 
Poles  of  cerebrum,  462 

of  eyeball,  563 
Pomum  Adami,  205,  425 
Pons  Varolii,  439,  460,  520,  533 
corpus  trapezoides,  545 
fillet,  545 

floor  of  fourth  ventricle,  542 
internal  structure,  544 
nuclei,  545 
pyramidal  tract,  545 


596 


INDEX 


Pons  Varolii,  raphe,  545 

reticular  formation,  544 
substantia  ferruginea,  545 
tegmental  part,  545 
transverse  fibres,  545 

Porus  opticus,  572 

Posterior  longitudinal  bundle,  513, 

533,  545,  546 
Precuneus,  473 
Preoccipital  notch,  473 
Pretracheal  fascia,  186,  208 
Prevertebral  fascia,  186 

region,  348 
Process,  ciliary,  567,  569 

facial,  of  parotid,  247 

muscular,  of  arytenoid,  429 

styloid,  304 
Processus  brevis  of  malleus,  555 
of  incus,  555 

cochleariformis,  552 

gracilis  of  malleus,  555 

helicis  caudatus,  270 

lenticularis,  of  incus,  556 

longus,  of  incus,  556 

vocalis,  of  arytenoid,  430 
Promontory  of  tympanum,  551 
Prussak,  striae  of,  554 
Pterygoid  plexus,  venous,  286 
Pterygo-maxillary  region,  279 
Pulley  of  superior  oblique,  336 
Pulmonary  orifice,  56,  66,  78 

plexus,  31,  32,  82,  83 

valve,  60,  74 
Pulvinar,  504 

Puncta  lacrimalia,  243,  277 
Pupil,  570 
Putamen,  518 
Pyramid  of  cerebellum,  538 

decussation  of,  522,  524 

of  medulla,  523 

of  tympanum,  550 
Pyramidal  lobe  of  thyroid,  240 

tract,  512,  520,  545 
crossed,  177,  524,  531 
direct,  177,  524 
Pyriform  fossa,  376 

Quadrate  lobule,  473 

of  cerebellum,  537 
Quadrigeminal  bodies,  461,  508 

brachia  of,  508 

Radiatio  corporis  callosi,  486 
Rami  communicantes,  grey,  92,  228, 
230,  320,  321 
white,  92,  319 


Raphe  of  medulla,  529 

palate,  366 

tongue,  433 
Receptaculum  chyli,  87 
Recesses,  lateral,  of  fourth  ventricle, 

541,  543 
of  pharynx,  374 
Recessus  epitympanicus,  550 

pinealis,  507 

spheno-ethmoidalis,  397 

suprapinealis,  507 
Red  nucleus,  514 
Reil,  island  of,  465,  480,  493 

limiting  sulcus  of,  465,  466,  480 
Restiform  body,  460,  527 
Retina,  564,  572 
Retro-pharyngeal  space,  368 
Rima  glottidis,  412,  422 

palpebrarum,  243 
Riolan,  muscle  of,  272 
Rivinus,  ducts  of,  301,  363,  365 

notch  of,  553 
Rolando,  fissure  of,  465,  466 

funiculus  of,  527,  531 

substantia  gelatinosa,  174,  524 

tubercle  of,  527,  531 
Root-ganglia,  166,  168 
Root-ganglion  of  vagus,  315 
Root  of  lung,  10,  30 
Roots  of  olfactory  tract,  480 

of  spinal  nerves,  166 
Rosenmliller,  fossa  of,  374 
Rostrum  of  corpus  callosum,  485 

Saccule,  562 

laryngeal,  414 
Salpingo-pharyngeal  fold,  373 
Santorini,    cartilages  of,   417,   424, 
429 

tubercle  of,  377 
Scala  media,  562 

tympani,  561 

vestibuli,  559,  561 
Scalene  tubercle,  193 
Scalp,  104 

blood  vessels,  111 

epicranial  aponeurosis,  106 

fascia,  105 

nerves,  107 

strata,  104 

surgical  anatomy,  112 
Schlemm,  canal  of,  566 
Scleral  sulcus,  566 
Sclerotic  coat,  564,  565 
Semicircular  canals,  559,  560,  562 
Semilunar  valves,  57,  74 


INDEX 


597 


Sensory  decussation,  531 
Septal  cartilage  of  nose,  389 

cusp,  58 
Septum  atriorum,  54 

lucidum,  497 

nasal,  387,  389 

orbitale,  275 

posticum  of  arachnoid,  162 

of  tongue,  438 

ventriculorum,  64 
Sheath,  carotid,  186,  202 
Shrapnell,  membrane  of,  554 
Sibson's  fascia,  16,  23,  226 
Sigmoid  valves,  57 
Sinus,  aortic,  68 

basilar,  126,  129 

cavernous,  126,  128,  323 

circular,  126,  129 

coronary,  49,  54 

costo-mediastinalis,  29 

frontal,  396 

intercavernous,  129 

laryngeal,  414 

lateral,  122,  126,  128 

longitudinal,    inferior,    119,    126, 
127 
superior,  118,  119,  126,  127 

of  Morgagni,  371 

oblique,  of  pericardium,  38 

occipital,  126,  127 

parasinoidal,  115 

petrosal,  inferior,  126,  129,  311 
superior,  122,  126,  129 

petro-squamous,  129 

phrenico-costalis,  27 

pyriformis,  377 

sphenoidal,  398 

spheno-parietal,  126,  129 

straight,  119,  126,  127 

transverse,  of  pericardium,  38 

of  Valsalva,  49,  60,  69,  75 
Socia  parotidis,  247 
Space,  interpeduncular,  454 

mediastinal,  23 

subarachnoid,  162,  441 

subdural,  117,  161 

suboccipital,  155 
Spaces  of  Fontana,  567 
Sphenoethmoidal  recess,  397 
Sphenoidal  fissure,  343 

sinus,  398 
Spheno-maxillary  fossa,  383,  401 
Sphenopalatine  ganglion,  401 
Spheno-parietal  sinus,  126,  129 
Sphincter  papillae,  570 
Spina  helicis,  270 


Spinal  canal,  157,  167 
cord,  164 

anterior  surface,  171 

arteries,  170 

central  canal,  173,  176 

ligament,  164 
cervical  enlargement,  164,  174 
columns,  173,  176,  177 
commissures,  173 
conus  medullaris,  164,  165 
cornua,  174,  176 
direct  cerebellar  tract,  177 
filum  terminale,  160,  164 
fissures,  172,  177 
grey  matter,  173 
internal  structure,  171 
lumbar  enlargement,  164,  174 
meninges,  159 
origin  of  nerves,  166,  171 
posterior  surface,  171 
pyramidal  tract,  crossed,  177 

direct,  177 
regions,  174 
segments,  166 
substantia  gelatinosa,  174 
sulci,  172,  177 
surfaces,  171 
tract  of  Burdach,  177 

of  Goll,  177 
veins,  171 
white  matter,  176 
nerve-roots,  166,  171 
nerve-trunks,  166,  169 
root-ganglia,  166,  168 
venous  plexuses,  154 
Spiral  canal  of  modiolus,  561 
Splanchnic  ganglion,  93 
Splenium  of  corpus  callosum,  485, 

488 
Stapes,  555,  557 
Stenson,  duct  of,  249 
Sternal  line  of  pleural  reflection,  18 

lymphatic  glands,  89 
Stilling,  canal  of,  574 
Straight  sinus,  119,  126,  127 
Stratum  zonale,  504 
Stria  medullaris,  503 
Striae  acusticie,  542 
longitudinales,  484 
of  Prussak,  554 
Styloid  process,  306 
Subarachnoid  cisternoe,  442 

space,  162,  441 
Subclavian  groove,  26,  29 
plexus,  321 
triangle,  1 90,  191 


59; 


INDEX 


Subdural  space,  117,  161 
Sublingual  gland,  298,  301 
Submaxillary  ganglion,  298.  302 

gland,  204,  298,  300 

region,  295 

triangle,  199 
Submental  triangle,  205 
Suboccipital  space,  155 
Substantia  ferruginea,  543,  545 

gelatinosa,  174,  527 

nigra,  511 
Subthalamic  region,  502 
Sulcus  or  Sulci,  of  brain,  463 

callosal,  481 

centralis  insula,  480 

of  cord,  172,  177 

coronarius,  44 

diagonalis,  471 

fimbrio-dentate,  482 

frontal,  469,  470 

fronto-marginal,  470 

of  Heschl,  478 

interauricular,  45 

interventricular,  48 

intraparietal,  473 

lateralis  mesencephali,  510 

limiting,  of  Reil,  465,  466,  480 

longitudinales,  of  heart,  48 

of  lungs,  26,  29 

of  Monro,  507 

occipitalis  transversus,  474,  477 
lateralis,  477 

occipito-temporal,  477,  478 

oculo-motor,  510 

olfactorius,  395 

olfactory,  472 

orbital,  472 

parallel,  478 

paramedial,  of  cerebrum,  470 
of  cord,  177 

parietal,  473 

post-central,  474 

postero-lateral  of  cord,  172 

post-limbic,  473 

precentral,  469 

rostrales,  472 

sclera?,  566 

stapedis,  557 

subclavius,  26,  29 

temporal,  478 

terminalis  of  heart,  45,  52 
of  tongue,  432 

tympanicus,  554 

valleculas,  535,  538 
Supraclavicular  region,  1S8,  191 

triangle,  190,  191,  194 


Suprasternal  fossa,  178 
Supratonsillar  fossa,  376 
Sylvian    aqueduct,    461,    506,    508, 
5io 

fissure,  462,  465 

grey  matter,  510 
Sympathetic,  cervical,  201,  203,  306, 

383 
gangliated  cord,  92,  201,  203,  232, 

306,  319 
thoracic,  92 

Taenia  hippocampi,  495 

semicircularis,  491,  492,  493,  502 

thalami,  503 
Tapetum,  486 

of  choroid,  568 
Tarsal  plates,  271,  272 
Teeth,  364 

Tegmen  tympani,  548 
Tegmentum,  509,  512,  545 
Tela  choroidea,  /\/\/\ 
Temporal  fascia,  112,  280 

lobe,  465,  477 

notch,  478 

operculum,  466,  478 

pole,  462,  478 

region,  279 
Tenon,  capsule  of,  331,  335,  345 
Tentorium  cerebelli,  122 
Thalamencephalon,  461 
Thalamus,  optic,  461,  492,  502,  520 
Thebesius,  valve  of,  54 

veins  of,  51,  54,  62 
Third  ventricle,  461,  505 
Thoracic  duct,  87,  216,  224,  311 

ganglia,  92 
Thorax,  1 

cavity,  10 

inlet,  2 

joints,  97 

lymphatic  glands,  89 

outlet,  2 

viscera,  10 

walls,  3,  93 
Thymus  gland,  38,  208 
Thyro-hyoid  membrane,  205,  415 
Thyroid  body,  207,  240 

cartilage,  424,  425 

notch,  425 
Tongue,  297,  431 

buccal  part,  432 

dorsum,  432 

frenum,  365,  433 

glands,  436 

mucous  membrane,  431 


INDEX 


599 


Tongue,  muscles,  435 

nerves,  437 

papillae,  433,  434 

pharyngeal  part,  375,  432 

septum,  438 

vessels,  437 
Tonsil,  366,  372,  376,  380 

cerebellar,  538 

pharyngeal,  372,  374 
Topography  of  heart,  65 
Torcular  Herophili,  127 
Trabecular  carneae,  56 
Trachea,  78,  207,  242 
Tracheotomy,  208 
Tract  of  Burdach,  177 

cerebello-olivary,  528 

direct  cerebellar,  177,  525,  528 

of  Goll,  177 

olfactory,  480 

optic,  454,  509 

pyramidal,  512,  520,  545 
crossed,  177,  524,  531 
direct,  177,  524 
Tragus,  270 
Transverse  fissure,  501 

sinus  of  pericardium,  38 
Triangle,  anterior  of  neck,  178,  198 

carotid,  199,  201 

digastric,  199,  204 

muscular,  of  neck,  199,  200 

occipital,  189,  190,  193 

posterior  of  neck,   137,  178,  187, 

189,  193 

subclavian,  190,  191 

submaxillary,  199 

submental,  205 

suboccipital,  155 

supraclavicular,  190,  191,  194 
Triangular  fossa,  270 
Tricuspid  valve,  57 
Trigonum  acustici,  542 

habenulae,  503 

hypoglossi,  542 

of  lateral  ventricle,  493 

olfactorium,  480 

vagi,  542 
Trunk,  dorsal  aspect,  132 
Trunk-ganglion  of  vagus,  315,  316 
Trunks  of  brachial  plexus,  195 
Tube,   Eustachian,   371,   373,   381, 

55o.  55* 
Tuber  cinereum,  454,  456 

valvuhe,  538,  539 
Tubercle,  acustic,  542 
amygdaloid,  493 
cuneatc,  527 


Tubercle,  cuneiform,  377 

of  epiglottis,  411 

of  Lower,  55 

of  Rolando,  527,  531 

of  Santorini,  377 

scalene,  193 

of  thalamus,  504 

of  thyroid  cartilage,  425,  426 
Tunica  chorio-capillaris,  568 

pharyngis  externa,  368 

Ruyschiana,  568 
Turbinated  bones,  393,  395,  398 
Tympano-malleolar  folds,  554 
Tympanum,  547,  550 

anterior  wall,  55 1 

floor,  550 

inner  wall,  551 

membrana,  547,  553 

mucous  membrane,  555 

muscles,  557 

posterior  wall,  550 

ossicles,  547,  555 

tegmen,  548,  550 

Umbilicus  of  tympanic  membrane, 

554 
Umbo,  554 
Uncus,  481 
Utricle,  562 
Uveal  layer,  572 
Uvula  of  cerebellum,  538 
palate,  366,  377 

Vallecula  of  cerebellum,  534 

larynx,  410 

Sylvii,  465 
Valsalva,  sinuses  of,  49,  60,  68,  75 
Valve,  aortic,  63,  64,  74 

bicuspid,  63 

coronary,  54 

Eustachian,  53,  55 

mitral,  63 

pulmonary,  60 

semilunar,  57,  74 

of  Thebesius,  54 

tricuspid,  57 

ofVieussens,  513,  535,  540 
Vein  or  Veins,  angular,  ill,  269 

ascending  lumbar,  96,  97 

auricular,  posterior,   ill 

azygOS,  major,  40,  96 
minor,  97 

bronchial,  31,  32,  87,  97 

cardiac,  49 
bral,  1 17 

cervical  dee]),  14S,  224 


6oo 


INDEX 


Vein  or  Veins,  of  corpus  striatum, 

491 
emissary,  128,  146,  327 
facial,  201,  238,  269 

common,  202,  204,  238,  311 

deep,  269,  287 
frontal,  in 
of  Galen,  500 
hemiazygos,  97 
infraorbital,  386 
innominate,  39,  208 
intercostal,  96,  151 

superior,  39,  96 
intraspinal,  158 

jugular,   anterior,    181,    192,    193, 
208,  231 

external,    180,    189,    192,    193, 

251 
internal,   201,    202,    216,    232, 

306,  310 

posterior  external,  181 

lingual,  201,  305,  311 

lumbar,  151 

mammary,  internal,  39 

mastoid,  128,  146 

maxillary,  internal,  286 

mediastinal,  40 

meningeal,  131 

oblique,  50 

occipital,  146 

oesophageal,  97 

ophthalmic,  330,  336,  341 

pericardiac,  40,  97 

pharyngeal,  311,  368 

posterior  condyloid,  128 

pterygoid,  286 

pulmonary,  31,  33,  60,  61,  91 

ranine,  298,  303,  305 

retinal,  573 

spinal,  154,  158,  171 

subclavian,  192,  216,  224 

supra-orbital,  11 1 

suprascapular,  192,  193,  223 

temporo-maxillary,  201,  251,  286 

Thebesian,  51,  54,  62 

of  thoracic  wall,  95 

thyroid,  inferior,  39,  207,  222,  242 
middle,  201,  231,  242,  311 
superior,  201,  231,  236,  242,311 


Vein  or  Veins,  transversus  colli,  191, 
192,  193,  223 
vertebral,  39,  221,  348,  353 
anterior,  222 
Velum  interpositum,  444,  491,  499 
medullary,  inferior,  539,  541,  543 
superior,  535,  540,  543 
Vena  cava  inferior,  40,  53 
superior,  40,  53 
magna  Galeni,  500 
Venas  vorticosoe,  566,  568,  571 
Ventricle,  fifth,  497 
fourth,  460,  521,  541 
floor,  522,  531,  541 
lateral  recess,  541 
roof,  541,  543 
lateral,  461,  487 
body,  490,  491 
cornua,  490,  492,  493 
floor,  491,  494 
trigone,  493 
third,  461,  505 
of  heart,  43,  47,  55,  62,  76 
of  larynx,  414 
of  Verga,  499 
Vermis,  534,  535,  538 
Vertebral  aponeurosis,  140 
Vestibule,  aortic,  64 
of  labyrinth,  559,  562 
of  larynx,  409 
of  mouth,  362 
of  nose,  388,  393 
Vestigial  fold,  38 
Vibrissa,  388,  393 
Vicq  d'Azyr,  bundle  of,  499,  520 
Vieussens,  ansa  of,  321 

valve  of,  513,  535,  540 
Visual  centres,  lower,  509 
Vitreous  body,  564,  573 
Vocal   cords,   409,   411,   412,   420, 

422,  430 
Vortex  cordis,  76 

Wharton,  duct  of,  298,  301,  363,  365 
Willis,  circle  of,  445,  453 
Wrisberg,  ganglion  of,  35 

Zonule  of  Zinn,  570,  574 


COLUMBIA   UNIVERSITY    LIBRARIES 


This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing,  as 
provided  by  the  library  rules  or  by  special  arrangement  with 
the  Librarian  in  charge. 


DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

C28  (747)  MIOO 

2002189070 


C912 
1908 
v.    2 


sal   anato 


9M22> 


C9/2. 

I90B 

V-2- 


